I have the m504 p304 combo and I agree with your impressions, this amp does not add a lot to the mix, top to bottom it is very clean, neutral and pretty well balanced. It can be on the bright side and good recordings are a must. I do like that with the p304 it is extremely quiet with no noticeable crosstalk. I read a lot of reveiws before I purchased mine on audio reveiw.com and I think most people love these units. Maybe it's the meters??? They sure are nice looking units. I have wondered if the models above the 504 are voiced the same??? I tried a yamaha M-60 with a carver c-2 and was pleasently surprised, nice tight bass, very little grain, surprisingly good imaging and depth. When I hooked up the C-2 to the 504 something sounded very off. Yamaha seems to make some nice amps!!!