No. I've had a lot of Mcintosh gear. I liked all of it, but it wasn't the best sound I've heard. I am not an Adcom fan at all, but the original 555 was a Nelson Pass design and it was (still is) an incredible amp. From what I understand the MKII is based on that same topology. Something you would really notice would have to be in the Threshold, Levinson, Krell, and Johnson camp. Then it may not really be much of a change depending on your music tastes and listening habits.
You don't mention your preamp. That might be the componet that you find lacking, as it would be hard to imagine that it's your amp.
