My situation, briefly... I have a very powerful AV amp which does everything I want apart from UHD and Atmos. The Audyssey XT32 room correction is excellent.
I thought I could get a lower powered (cheap) atmos receiver and use the multi-channel output to feed this amp, using the low powered amp to just power the atmos speakers. However, one technical limitation of the old amp is that room correction is not applied to the multi-channel analogue input, only to digital sources, so it would end up as a dumb amp.
Then it occurred to me that I could feed the old amp with LPCM sound via HDMI for the conventional 7.1 channels (after the new AV receiver has decoded the Atmos channels to analogue, which could be tapped just before the power amp section). The problem with this is:
1. No 8 channel input audio grade ADC that doesn't cost silly money for a PC.
2. No 8 channel audio grade ADC for RasPi at all.
3. PCs don't decode Atmos (7.2.4) at all, and it looks like it won't happen in the near future.