I have about 2200 CDs ripped on an external hard drive in FLAC 24/48.
CDs are 44.1kHz, 16 bit (16/44.1). If your ripping process has resampled these to 24/48, then it almost doesn't matter what you do, as the original information is gone.
If you actually have 16/44.1 rips, then I would try running without any conversion. Then maybe try it at 192kHz. I suspect you won't hear any real difference, but maybe?
If you have the standard or "uber" Bifrost, then all of this applies. If you have the multi-bit Bifrost, then you absolutely should NOT resample. Just send the data exactly as is, with no changes at all: No DSP of any kind.
Brian.