Short answer, don't waste your time.
Hi Fi Drivers are high Compliance while MI Drivers are Low Compliance so they are worlds apart.
Hifi woofers rely on a defined space, a sealed box with or without a tuned port.
They will just wobble outside of a defined enclosure. They are mostly much lower on SPL levels. They give close to zero hi frequency while passing full range signal.

MI drivers can work in open or sealed boxes, I'm old enough to remember small pa speakers just mounted on a flat baffle board with no sides and a couple of angle brackets to hold them in a vertical position.

On the other hand keep your eye out for older hifi speaker boxes which used Low Compliance speakers as some will be able to reproduce a half decent sound for small guitar amps. don't expect them to handle hi power amps as they are very old and most will be low wattage.

Easy to see the difference as most hifi Woofers have a big rubber spider around the edge while low compliance driver will have the rippled spider often made of cloth or tarred paper.
Phil.

Thanks Juan,
            At least I have several recording of my wife singing that we recorded some years back. I'm so glad that I persuaded her as she was a trained singer with a unique tone and range. I was able to play one of her recording at her Funeral which got a huge response.
Now I just sing at open mic jams, the music keeps me sane.
Phil.

Thanks Joe,
Yeah, If I didn't already have a sound/tone pedal board that I'm quite happy with then I would certainly check this out.

Using Analog circuitry for cab sims and amp parts is likely part of the reason it sounds good. Full bore dirt is a bit weak in the low freq but hard to judge when it's recorded on a phone.
Reverb sounds ok.

Certainly far more usable than a lot of other pedals. (what happened to the thumbs up emoji??)  

The one sound a lot of these fancy pedals can't seem to crack is that magic sweet Santana lead tone, which delivers a huge cut through without the brittle irritating top end fizz. I'm yet to hear that done.
Phil.

Also with power on gently pressing on the board in different places
(with an insulated probe) can help track down an offending component.
Phil.

Ahh yes nothing worse than intermittent crackles.
Yes a component dying or a cracked or cold solder joint,, my guess you have a cracked track hiding in the maze.
Get yourself a wooden skewer stick and while amp is on gently poke and move components on the PCB. you can get lucky and find the part that is causing the drama. The bottom side will not be easy to access so disconnect an pull the board out then with a magnifying glass in bright sunlight go looking for hair line cracks, especially around the solder pads.

I actually own a SS Laney amp, even earlier model that yours and it developed a crackle last year which drove me mad but finally found a hairline crack which was actually hidden by a solder lump so Even with magnification you could not see it.
Keep us posted, Phil.

Some helpful info here: https://ozvalveamps.org/varidamp.html
variable damping been known way back.

Front page; https://ozvalveamps.org/
Site setup by a wonderful Aussie Roly Roper, sadly no longer with us but His site is a credit to him as he lists most of all the Aussie Valve amps that were made in Au and NZ.
With tons of good advice from a highly experienced Teck.
Phil.

Re Current Feedback also called "Defined Impedance" of an amplifiers output.
Most SS HiFi DC Poweramps have a very high Damping factor. No over shoot of the Cone, The speaker follows the signal as perfectly as the laws of physics allow.

Ye old Valve Guitar amps tend to have low damping factor. The cone over shoots more. Partly due to the Output Transformer. Also remember every time the speaker cone moves it also generates it's own energy Called Back EMF. High damping reduces that effect.

CF is no magic bullet yes at high volume you may notice a little benefit not so much at low volume. If this Amp has an output TX then you already have the best setup and little benefit will be had by implementing CF. (and likely more complicated because of the OTx)

Rod Elliott has lots of mind bending info if you wish to know more
https://sound-au.com/articles/cfb-vs-vfb.htm

Home page here; https://sound-au.com/

Now Others here will know far more about this interesting subject and Some claim great benefit but for me having messed with this stuff years back there is only  marginal benefit and I doubt if you are loud and live on stage you would hear much difference.

There are tricks you can implement with CF that can alter the Frequency response, may be of benefit,  Peavey implement CF in a lot of their circuits as do many others.

Warning As With any TX coupled output make sure you have a load on the output before you crank up the volume.

If it was on my bench I'd be using a stand alone preamp or some pedals first as messing with the unit directly might reap little rewards. just  a thought?

Regards Bridging Amps,,, cricky just get a chip that delivers the Wattage you want and save all the messin around.
Member J,M,Fahey has designed and built likely 100s of SS guitar rigs and a lot of those use OTx. Good to see that he is still posting
He will have a lot to say about the advantage of using Tx coupled outputs on SS rigs.
Phil.

Yes you can use an attenuator on SS Power Amp but there is little benefit as most of them run much cleaner that a Valve Pwramp.
With SS rigs 90% of the OD effect is done in the preamp stages.
whereas with Valve rigs you can get extra sag and compression just from driving the Amp LOUD. Hence they use Attenuators on Valve amps to get the pwr section in sweet Spot But at reduced Volume.
The only time I use an Attenuator on SS amp is for bench testing a circuit under load, to make sure it can actually handle sustained full power.
You have a Master Volume on Rods Circuit and that will do the same as an Attenuator.

The diode Clipper before the Master Volume in Rods circuit is unlikely to give you full bore Screaming OD/Distortion.(If that is what you are chasing) You would need to drive it all with pedals if you want more Screaming OD.
Phil.

I lost my Wife last year And 20 years earlier she lost her son to suicide, she carried on but it left a mark on her outlook on life.
Yes the things that life throws at us can be soul destroying.
So I have some understanding of your great loss.
Phil.

I don't believe I mentioned Diodes as you don't need them,, maybe I'm having a brain fart? (head scratch)
 What you have is correct but Add a low value resistor before the Send otherwise the previous opamp output could get a dead short at some point.
Frankly there is no great benefit I can see to add the Loop, just plug in to the front of the amp,,,, but your choice.
Phil.

Yes 10uF to Ground is fine.
Just google "Smokey Amp Schematic" will give you many schematics using LM386.
Have fun with it.
Phil.

Great to hear you fixed it. Good work G1 
Phil.

To me that points to a possible cracked track or cold solder joint.
As it heats up the joint expands and high resistance causes the volume to drop.
With chassis out Gently and carefully probe/press all over the PCB and/or wire connections (With a wooden stick) and see if you can find which joint has failed.
Valve socket solder joints are often prone to fail like this as they cop a lot of heat as well as movement when changing Valves.
Phil.

Well if the Amp hums Instantly then set meter to DC and measure how much DC is on the output.
It should read very low, in the millivolt range.
If there is large DC voltage at that point then the power amp has failed.
It's Best to disconnect the speaker otherwise you can burn out the speaker coil.
Better minds here maybe able to help you test some voltages in the poweramp section.
Phil.

Those Voltages are correct, you just measured them in the wrong place.
68.2 divided by 2 = 34.1 which is close enough to spec.
You just measured across both + and - Voltage rails, forgot the common center tap.
Same with low supply, 29.4 is the potential across + and- rails.
Both Preamp and poweramp supplies use a split supply where you have 3 wires from transformer the center tap is the common or Zero point.
Sadly none of this helps much as the amp is faulty.
There looks to be a mute circuit hung off pin 6 of U1b consisting of Q1 & Q2 which may have failed causing very low output.
Other here will know more.
Phil.