FLAC works the best in displaying metadata correctly on MPD. I've compared it to ALAC, AIFF, and WAV's metadata displayed. WAV is the worst. FLAC gets it right. Krutsch has also ran into issues with how certain fields are displayed differently with different formats.
James has always recommended FLAC as the preferred format. He or Bryston has never said anything compressed or uncompressed.
The only "controversial" thing James has said about it is the flash drives perhaps sounding better than hard drives. He acknowledged that Bryston engineers don't really agree with him. He's also suggested using internal connection over attached connection to bypass the USB connection.
Regarding, compressed and uncompressed, you can get FLAC in compressed and uncompressed. Same metadata on both. The uncompressed is the same size as AIFF and WAV. I personally went with WAV as I didn't care about metadata since I had the Bryston database and other things disabled for the lowest CPU use. WAV sounded right.
If you want to reduce the load, I'd go with Roon. Roon consumes less than MPD even when MPD is running at its bare minimum. Roon also sends PCM to the BDP, so there is zero decoding going on in BDP. With normal MPD use, there will always be decoding taking place inside the BDP regardless of compressed or uncompressed. That's why I went with uncompressed.
Roon sends PCM via ethernet. So you can use compressed FLAC or WAV and BDP will see the same thing (PCM). So you can save space and time only having to maintain one library. For peace of mind, I've compared FLAC against WAV through RAAT and it's the same. The metadata support is on whole another level altogether to Manic Moose.
Roon also sounds the best IMO.
(I did have to play around with how I setup the ethernet routing for best SQ, but that may not be required for everyone. It could be system/situation dependent.)
EDIT: James replied while I was typing.
