To be honest, I dont know. GB-PVR simply downloads the data, removing the headers to save it as an MP3 file. Your question more relates to the MP3 codec installed on your machine, and what is capable of playing.
I know there are some bitrate MP3's that the MVP wont play.
Thanks - don't worry. I was trying an experiment - an old trick Netgear MP101 users use to transcode non-MP3 Internet Radio streams using Winamp, Shoutcast DSP plug-in & Shoutcast DNAS as a localhost server.
The GB-PVR end is working fine - but it appears I'm creating 'silent' MP3 files with the convoluted setup mentioned above.