Spud, if you search for a graphic EQ with 2 outputs to drive either 2 different sound chains or 2 amps, maybe have a look at MXR m108 Kerry King. It's 10 bands, have a pre gain and post overall level, have 2 outputs...
Sounds promizing, even if a bit pricey.
What's interesting is that you have the 2 most bass bands outside of typical guitar range. Might look unneaded, but it's an opportunity to cut completely (well, not completely but -12db is pretty significant I would say) these unneeded frequencies and therefor help your amp dealing with only what really matters. Same in the high range with 8 and 16 Khz. Use the rest of the bands to fine tune how your signal will be presented to your drive.
In my recent testings, I found that there is a lot to do with pre-dist EQ, not in terms of general EQ, but in terms of what part of the sound your dist will clip/compress.
I'm currently simulating some clipping on complexe signals made of several harmonics (guitar signals are NOT sinusoids, even when playing single notes, and obviously more so when struming chords). I'm not at the point where I can present some results, but it's really interesting how filtering some of the harmonics and frequencies produced by the guitar before clipping (I'm using a square hard clipping for simulation purpose) does affect a lot the wave form of the resulting signal.
Clean boosting has its merrits, but if you can combine it with some alteration of the EQ in the same time, you're golden.
Another thing to try would be to insert a soft clipping slight overdrive adjusted to just barely clip the heaviest strummed chord you can make before your amp. This retains a lot of dynamic variations. Then you set your amp dist to clip a bit before that. You know have access, just with the power of your attack on the strings to:
- clean and clear tone when strumming really gently
- various amounts of distortion, in proportion with your attack
- a really fat tone with lots of sustain when both stages clip
This is really subtle to adjust, but if your overdrive as a different colour to what your amp does and you are able to control your attack, you will be able to have a lot of variety in how each note sounds. It's also super usable for "let ring" arpegios: the attack might be clipped, but as the note decreases, it becomes cleaner and cleaner so you have both sustain and clarity. Combine this with intellingent EQing before your clipping stages (actually, even the tone pots of a guitar are a really basic sort of pre-dist EQ) and you will find that your amp might produce impressive tones. Well, this might cost you a lot of time to experiment, but I'm pretty sure the results will be worth it.