NAD is going to be more rounded and laid back sounding - perhaps the most neutral of the three. Cambridge is going to be more forward and "exciting" sounding, but 640 is a more capable amp than the NAD C320 (might want to look for an NAD C352 as Internet closeout for under $500 and packing 80W as alternative). I think the Music Hall is the highest quality amp of the three, with more solid build and decent sound. Suggestion about the Creek is interesting.
NAD vs Cambridge audio vs Music hall
I am a college student on a limited budget putting together my first real system, i have found a pair of totem dreamcatcher monitors and have a small sub to go with these speakers, i have posted forums before, asking about cheap tubes vs ss etc. i think at this point i am going to go with a ss just because of the fact that i still have a year of school left and that im not all that experinced and dont know if im ready for the 'maintenance' of tubes right yet. I have narrowed my choice down to 3 budget integrateds, the NAD c320bee ($400 new), the cambridge audio 640a ($479 new), and the music hall A25.2 ($600 new), unfortunately i do not have the ability to demo any of these. I apreciate all recommendations and and experience that anyone has had with any of these amps................ thanks