After much messing around (damn you and your short speaker lead evo 1) I can confirm that the evo 1 through the evo 2's speakers is just as loud as through it's own speakers and so the problem obviously lies with the evo 2 amp.
After messing around some more I'm starting to think maybe the original evo has slightly more bass.
I've also noticed that with the compression on, regardles of the setting, there is a noticable overall boost in volume. While i dont know very much about compression, I'm wondering if the built in compressor has some kind of 'make up gain' applied to it automatically and to counter this, the design of the evo 2 amp is quieter as a result. Which obviously sucks if you want a lot of voulme but dont wan't to use the built in compression. Seems a bit crazy to me but i guess it's possible.
I'm going to give it another whirl at practice this week and see what happens. Hopefully when my neighbours go out, i can try the evo 2 driving both sets of speakers together
I'm starting to think it's less of a fault and more a difference in design. I can't help thinking if it was a fault with dirty connectors or something else, the sound quality would be noticable worse, and it isn't. it sounds great, just quieter.