Has Anyone Compared the 2 McIntosh Integrateds?

I recently purchased the MA6500 and have been very happy. According to an email response from McIntosh tech support, the MA6500 is a combination "C15 preamp and direct coupled version of the MC202 amp." The MA6900 is described as a combination of features from the C42 and MC202. I have not been able to audition the MA6900. I would think any sound quality difference would be more dependent on the type of speaker used and its impedence plot. I would think the 6900 would handle low impedence / low sensitivity speakers better because of the autoformers. With easy to drive speakers (I'm using Spendor s3/5 - 8 ohm) I can not see the benefit of the autoformers outside of DC protection. The Sam Tellig review in Stereophile claims that the MA6900's output transitors "look for a load of 2.9 ohms before the signal goes to the autoformers." Therefore, for easy to drive speakers 4 ohm or greater, I would expect less benefit from the autoformer. Again, this is only confirmed with audition. Either integrated delivers more power than I need. As I leave tone controls in bypass mode, the c42 based preamp is not a personal need.

According to my manual for the MA6500, power output per channel is 250 watts at 2 ohms, 200 watts at 4 ohms, and 120 watts at 8 ohms. The question of ability to drive large Magnaplanars can only be answered based on the size of your room and the volume level of listening. I would expect either amp to drive the speaker in most reasonably sized installations. The 6900 may run cooler with lower impedence speakers, but if the 6500 was not enough power for the room, I'd expect that neither would the 6900. I would expect a larger external amp would be more appropriate. A switch on the back of the 6500 allows connection of an external amp instead of, or in addition to, the built in amp.
Good deals on the MA6500 via Audiogon classifieds and ebay have appeared. I bought mine in new condition via Audiogon for $2250. One sold for less on ebay a few weeks ago. Being so new, I have not seen MA6900s available on the resale market.

Not only are tone controls defeated at the center position, but "All tone control circuit elements are removed from the signal path when the controls are in the center or flat position." ...MA6500 Manual.