Sorry James, I don't agree with your reasoning.
I have spent approx. $28,000 on my multi-channel, HT. Based on having had an SP2 for a year, to achieve a equal level of sound quality I would need to spend approx. $18,000.
However the real difference is it would have taken me 10 years to acquire $18,000 to plop down on a quality stereo system. A rich man can do this but can he truly call himself an audiophile?
Instead I built progressively as I could afford, listening and learning where improvements in sound could be had and purchased accordingly. Every upgrade improved the sound.
Now that I have the SP2 I can make a fair comparison between 2 channel, multi-channel stereo and surround sound.
Not having an ideal room dimension wise, I can honestly say there is not much difference between quality 2 channel an quality multi-channel stereo. It really depends on the mix and is a preference thing as to which is better.
However, a good multi-channel sacd recording and mix trumps everything I've listened to in stereo.
Bottom line though is a quality recording. I'm shocked to learn lately listening mostly to 48k dvd's switching tracks, that quality recordings existed from way back in the 60's. But the formats, intentional or un-intentionly marketed inferior sound. 
Your logic makes zero sense, either that or you are not accurately representing yourself. You said that you spent $ 28,000 dollars to get multichannel audio/HT, but would need $18,000 to equal it in stereo, which is significantly cheaper, and PROVES James' point.

The bottom line is, James is fairly correct. IMHO, there is no processor on the planet that can equal a well designed, well built, vacuum tube preamplifier.
Not to mention that the DACs that are being run in these processors are not up to par either compared to a quality external DAC.
For the 7-12K these high end processors are selling for (which will also be obsolete shortly because the HDMI standard changes every year to generate mass market receiver sales), you could purchase a very nice tube preamp (the TRL Dude off the top of my head), plus a sweet DAC (PS Audio PWMK2, Lampizator, Etc, Etc), and kill the processor in terms of musical reproduction and realism and dimensionality in 2-channel.
Not to mention you could also, given the same budget, lets say 28K, buy significantly better main speakers, without having to sacrifice to include a center channel, and how many ridiculous channels they are advocating for now. 7.1? 9.1? 11.1? 13.2?
Not to say that multichannel can't be done right, its just a lot more expensive, hence James' point.