My guess is that the 6600 is better than the 6900 because the two new integrateds are based on the Reference circuits. The 6900 was a great amp but you had to be careful to match it to speakers that weren't soft or slow. The 7000 is not that way at all - it has "get up and go" that the 6900 never really had. I'd say the 6600 is very similar to the 7000 circuit-wise.
As for C220/252 or a 7000, that is a tough call. I think I would go for the separates but that is me. I like the felxibility. However, one thing I didn't care for with the C220 is that the controls aren't as nice as the higher level Mcs. It seems to me there is some obvious cost cutting on it. For example, the volume control doesn't feel nearly as nice as my C42's (or the C46 for that matter). Also, when you change inputs, the clicks are "tinny" sounding whereas the other preamps sound like solid and well-damped clicks. Any way, minor stuff I guess but kind of important to me for a preamp.
Arthur
As for C220/252 or a 7000, that is a tough call. I think I would go for the separates but that is me. I like the felxibility. However, one thing I didn't care for with the C220 is that the controls aren't as nice as the higher level Mcs. It seems to me there is some obvious cost cutting on it. For example, the volume control doesn't feel nearly as nice as my C42's (or the C46 for that matter). Also, when you change inputs, the clicks are "tinny" sounding whereas the other preamps sound like solid and well-damped clicks. Any way, minor stuff I guess but kind of important to me for a preamp.
Arthur