Yes, we use 8" speakers because they break up quicker (ie. at lower volume) plus they aren't too bass heavy. I use speakers salvaged from old electronics. So far, the best I've found are 8" speakers from old organs. Great Tone! Some people report that the cheap Jensen MOD series 8" sound good for harp, and others will swear by Webers. I get my vintage speakers for about $5-10 bucks each, versus ~$25 for the cheapest new speakers, but you definitely will have to put the time in and search around to find those old drivers. Read the reviews of various speakers at this blog: http://bluesharpamps.blogspot.com/ He reviews both Jensens and Webers, and is thought to be a reliable source.
And yes, Adam mentions the 8" speakers in that vid.
And yes, Adam mentions the 8" speakers in that vid.