I, too, have only heard good things about the MA 6100 integrated. When I look at the internals of it -- in the McIntosh Compendium -- I see a lot of similarities to an old favorite of ours: the Mac MAC4100 receiver. I suppose it's true, any stereo amp or integrated could be beat on and, in the end, it has a lot to do with how much heat it's been subjected to over the years. Our MAC4100 and our MAC 4200 still sound fantastic and they're nearly as old as the subject of this thread. We've moved toward Mac separates over the years, but, if not abused, most of their stuff should provide great service for many, many years.
On the other hand, I haven't heard a Scott 299, so I can't really make a fair comparison. I suspect that Audio Classics will do a great job...they usually do...so I wish the reverend all the best with his A/B testing. It would also be interesting to read his results.