"What is your optimal bit-rate when playing a digital file?"
Mumbo Jumbo numbers are not the rewarding path to the promised land. There are certain hard facts out there:
(1) No matter what else you select MP3 versus an uncompressed PCM digital format is like comparing a mule to a thoroughbred ... 'nuff said.
(2) The vast, VAST, majority of digital recordings are CD quality 44/16. XRCDs make a huge improvement difference (assuming that you have the kit that will make use of the resolution step-up). It is essentially "proper" CD quality recording with the compression and other related crap removed (usually introduced for airplay)
(3) A high-end QUALITY DAC playing at that "44/16 will generally smoke a cheap(er) unit that claims to upsample to a higher level and get better results
(4)Using a cheap PC and a cheap cable as your source is OK BUT a hi-end digital player matched to the DAC (e.g inter alia BRYSTON / LINN / NAIM)is not an insignificant improvement either.
(5) There are some good articles out there, for example:
Why some high resolution music isnt worth the extra dough
ttp://www.digitaltrends.com/home-theater/when-high-resolution-audio-isnt-hd/#ixzz2xw839C7s