@benanders, I have. I am.considering one for my 7.4.4 movie room in the future. I want this to be strictly 2 channel system.
I would never discredit a high quality multichannel prepro for 2 channel listening. They are designed for the pros/integrators (though they have been made available for the average end user these days), i.e., require you to go through a steep learning curve and have significant knowledge base as a end-user. But, if you are able to overcome that learning curve, it is the best tool that exists for 2 channel listening in execution.
Here are some tools that it would offer depending on the brand you went with....Pristine bass management (if you chose that route) or all kinds of tools for blending in a sub. Ask a dude to blend in one subwoofer with a purist preamp. He will struggle. Now, ask him to blend 2 subs. He will struggle a whole lot more. The prepros also offer very accurate time alignment, PEQ, parameters to modulate the soundfield to taste, etc (an endless number of tools), cater things for your specific room and your ears.
Multichannel gear falls apart when you stuff 9 power amps in the same chassis (i.e. the receiver!). But, a prepro processor designed from the ground up with no amp channels, paired with a high end "audiophile" power amp will fix that type of nonsense. The purists fiddled with a barrel bottom receiver and claimed that multichannel gear sounds like buttcheeks next to their supposedly great 2 channel purist gear.
For example, i own an engineering marvel of a prepro from yamaha called the CX-A5200. I also own their 10k purist preamp and a 20k Luxman preamp. If i paired a high end purist poweramp and subwoofers with the 3 above mentioned units and did side-by-side comparisons to dudes, the results (in execution) would be startling to such dudes.
It would be very hard for the average dummy designing/touting purist gear to design a prepro (It would be way too complicated for his wet noodle cranial compartment). Purist design philosophy is all about selling the same sht to the same group of disgruntled/unsatisfied customers over and over (keeping them disgruntled/handicapping them by removing all useful tools for sound reproduction in a room).