Splitting the signal should not degrade sound quality, as long as you use a reasonably well made splitter. You may need to adjust the left and right surround channel trim settings on the BD50, as the act of splitting the signal will reduce both divided signals. The adjustment is likely to be +3dB on both left and right surrounds, although I'd personally prefer to use a calibration disc's test tones and an SPL meter to verify that.

I think the word you are looking for is "marketing" - a receiver or processor that does not offer 7.1 support is going to have a hard time in the marketplace when all of its competitors do offer 7.1 support. And to be honest, the processing options available to generate 6.1 or 7.1 content from 2.0 and 5.1 sources are pretty extensive and widespread. Dolby and DTS both make sure to have equivalent algorithms (again, "marketing" is significant here, although it's not a bad thing - competition in the marketplace improves both companies' offerings). The only case where you see limited adoption is on source material, and I have a hard time complaining too much. Adoption of DTS 5.1 was slow enough that it's hard to be surprised DTS-ES Discrete didn't catch on, and I'm not terribly overwhelmed by Dolby EX (a Dolby 5.1 track and PLIIx is pretty effective, after all, and works with any ol' DD5.1 source). That just leaves the three new formats - Dolby Digital Plus, TrueHD, and DTS-HD - that can offer more than 5.1, and all were tied to a messy format war until earlier this year in addition to requiring changes in how audio mixing is done. That means studios had to decide to invest money and time in order to create 7.1 tracks that only work with formats that were caught up in a format war (coming just a few years on the heels of a format war in which both sides "lost" for all intents and purposes) and for a limited customer base. After all, many people are doing well to just get five speakers in their room - much less the seven needed to use that more expensive mix. That last issue - limited number of 7.1 systems - is likely to be a big reason that 7.1 mixes don't become standard. Here's an example: I work in an office of close to 15 people, most of them engineers. Out of that group, three have home theater systems with separate processors and amps as well as very nice speakers. Of the three of us, only one has a 7.1 system - the others are 5.1 and 3.0 (although the 3.0 setup may finally move to 5.1 before long). So of the 15 people who might buy movies, only one would benefit from a 7.1 mix - and even that one (me) would only benefit if he had a player with 7.1 analog outputs or a processor with HDMI v1.1+ input, which is not currently the case. So, basically, none of us could properly use a disc with a 7.1 mix at present. In contrast, those same 15 people include at least five HDTV owners, at least two of whom already own Blu-ray players.