Like I said, you don't have to have it - the 790 would still work if fed from a single 15A circuit, it just wouldn't be able to produce the full 300W from all seven channels at once (which would be an improbably demand anyway). And no matter whose amps you buy, if you want to have seven channels with 300W each and the ability to push them all tho that level, you've going to need those two separate circuits anyway since a single 15A circuit can't provide that much power.

I've never messed with my 750's fuse, so I don't know what size it is.