You should never transcode to a higher bitrate. And it’s best to convert from a uncompressed and lossless source. Those are the only two rules of thumb. What you convert to will depend on the complexity of the music, your hearing, and how picky you are.
I'm still in the digital learning stages, so please go easy on me. At this point, we have an intranet (non-internet) LAN setup and we're experimenting with JRiver MC28 for Mac as our audio media server software application.
Long story [a bit] shorter, we're sending flac audio files over the network to our streaming devices -- Oppo 105D and Sony X800M2 -- and, invariably, they are displayed on our video monitor (our TV) as being played back as .mp3 at 128 Kbps. Is there a utility out there that can tell you which format you're listening to? I'm asking because we've put many years into buying some pretty decent audio equipment and I'd like to think that our music is remaining as bona fide and true to the source material as possible.
If this isn't making any sense or, if I'm in the wrong place, please let me know.