I have owned both the MA6500 and the MA6900. I upgraded from one to the other. They are both very fine pieces and you should be happy with either one. The reason you don't see much press is that McIntosh historically does not market their equipment to the media outlets. However, this is starting to change and you see a lot of reviews of the MA6900 these days. You also don't hear much from peers because many audiophiles shrug off any mention of McIntosh as worth considering. I was originally drawn to it because my grandfather had it and it was also one of the most musical amps I heard (and I auditioned many). A lot of non-audiophiles also buy McIntosh because of its reputation, convenience, and ability to be placed in custom installations. These people tend not to lurk around audio forums so you can't hear their feedback, and many of them may not have a critical ear either.
I upgraded to the MA6900 because I tend to keep my audio equipment for the long haul and I preferred the sound of the autoformers and appreciate the equalizer. This amp just sounds spectacular over a wide range of musical styles. The MA6500 was nearly as good, and some would argue that the extra $1500 for the MA6900 is not worth it. Either amp would be fine for you if you like the sound. It is frustrating to me that there are so few high-end amps that have tone controls. I'm running my system in a large room and I appreciate being able to boost the bass and lower-mid range to increase the low-end response. Sure, it's nice to hear the music as-is, and the McIntosh amps can do this because in the center position the tone controls are out of the signal path, but few listening rooms are perfect and some compensation comes in handy. The MA6900 is very musical while still detailed enough for my ears. So many amps I listened to were hyper-detailed which was interesting, but ultimately fatigueing and many of them were too bright in the high-end.
For reviews, also see Hi-Fi News and... oh, I forget the name of the magazine, but it's a current issue (both British). Hi-Fi news called the MA6900 a dream and a bargain to boot. But the press has focused on the MA6900; the MA6500 is almost equally deserving of praise in my opinion. I'd say you can't go wrong with either.
