Exactly this. More and more discs have an Atmos mix now, so using anything other than bitstream would be plain stupid.
I've also yet to come across an Blu ray with both Dolby and DTS lossless codecs - it's one or the other, increasingly Atmos/Dolby True HD. Sometimes in the set up menu on the disc there will be an option for 2.0 PCM as well. But why anyone would chose that above a multichannel Atmos mix is beyond me.
You might get older titles remastered with a selection of audio options, such as original mono or 2ch stereo, further upmixed with quad or 5.1 or 7.1 options too.
I like to play older movies at times in their original mono or stereo through my stereo kit.
Perhaps that choice bewilders you too :0)
I haven't got Atmos, or even 7.1. Atmos to TrueHD is default through my kit with the 7.1 downmixed into the 5.1. So I think the questions exploring a potential benefit for pcm over bistream is valid as an idea.
Or are we all just stupid?
Yes, there are still folks out there using plain 5.1 or stereo (christ, even some of us still watching dvds and wanting them in the correct ratio right across our 16:9 screens - nods to the 9000 thread argument).
I don't know if older gear would have an advantage in outputting lossless codecs to pcm first, but it's a possibility that I haven't been able to nail down as any kind of consensus. Whatever works best is always, er, best.
So, if it is true there's no difference between lossless bitstream and pcm, as is oft claimed, there should be no problem converting to pcm at source, rather than amp, and if the amp does pcm better than bitstream, it would be...best.
That possible setup may be beyond you, I'm sorry about that. But us troglodite luddites (for that read just not paid enough to afford the latest Atmos setup) can occasionally still have outmoded ideas that aren't necessarily negated by the fact that some people have tech that is superior :0) (jealous)