I can't speak for the 750, but I've owned a separate amp for about 5 years. Its 125x5 and packs some punch. I had it hooked up to an old HK receiver initially and the net result was much more distinct and clear sound at lower sound levels and much higher usable sound levels.

I have since hooked the 1050 to it and experienced the same benefit. To be honest, though, I have never even used the 1050's internal amp, so I can't comment on the specific difference with this receiver.

Gonk has used the 1050 alone and with the 750, so he is really the man (as well as some other people I don't know of, probably) who can wholly answer your question.

S.