I'd grab the b-stock, and put the savings towards a good 4K disc player. If you're truly going for audio/videophile nirvana, then disc is the only way to go. No comparison in terms of bitrate, especially on the audio side (think MP3 vs FLAC). 4K UHD discs can be had for fairly cheap on Ebay (I spend $20 per movie on average).

Axiom M5HP VP160 M3 ADA1000
Anthem MRX 720
SVS SB-3000 (dual)