I got this reply from imerge:-

Dear Chris,

The Imerge NP200 requires an Imerge S2000 SoundServer as an audio
source, not a PC, to supplement it's internal AM/FM radio and the
Internet Radio functions.
The S2000 and the NP200 can both only decode WAV and MP3 files
(128/160/192/192VBR/320 Kb/s) and this is unlikely to change for the
foreseeable future.
You can transfer these file formats from PC to the SoundServer using
XiVA Producer Software.

If you have any more questions then please do not hesitate to contact
us.

All the best.