I have owned a set of the 107/2 since 1992, and compared the 107 and 107/2 in the same system at the time of purchase. I thought the 107 and 107/2 had a very similar overall sound, although the 107/2 was somewhat more transparent in the upper frequencies. Overall, I thought the major weakness of the KEF 107 was that it was a little dark, and the 107/2 reduced (but did not eliminate) that weakness.
While the MA6500 is a fine integrated amplifier, I have found that the 107/2 like a lot of power. My recommendation is keeping the 107s and upgrading to a more powerful amplifier --- the McIntosh power amplifiers with autoformers work great with the KEF 107/2, and I suspect would be a very nice match for the KEF 107. If you find that the McIntosh autoformered power amplifiers (which lean a little to the polite side) and KEF 107 are not lively enough, a Bryston 4B SST would also work well.
