customer requested--some notes from him:
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I was playing a whole album FLAC with an external cue sheet
(very nice that this works!) and noticed that
a track with FLAGS PRE (preemphasis) didn't decode with
deemphasis set on my external DAC.
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Some (rare) CDs are encoded with pre-emphasis.  This,
in effect, runs the sound through an equilization curve (when recorded) that must
be undone when you play the CDs back (or they will sound shrill).
There is a bit on the cd that indicates this.  When you extract a CD
to a cue sheet, this shows up as "FLAGS PRE" on a per track basis.

CD players do the deemphasis automatically as it is part of the red-book standard.

I'm not sure of which audio file formats support storing this preemphasis
bit.  WAV certainly can't.  mp3 might depend on the encoder used
(I think lame does, see -e option).  I couldn't find an option in FLAC...

In any case, since you can play using a cue sheet (a *great* feature)
I think SS should using the FLAGS PRE as specified in the cue sheet.

In grep'ing around the slimserver sources, I didn't find any mention
pre emphasis feature.  So, I'm guessing that you don't handle it

However, it is checked for in the CPAN module that you use for FLAC.