Here's another couple of questions for you, Ian:
If I have a 16-bit stereo 44.1kHz MP3/OGG/WAV, and I play it back at 32-bit 96kHz (or as near to that as the sound card goes), what happens to it. Does the interpolation affect it at all?
Also, I have a little problem with OGGs & XMPlay - I create a OGG (typically ~152kb/s) from a WAV file (that was from a CD), all at 16 bit 44.1kHz, and then play it back with XMPlay. When I play the OGG, XMPlay decides that 64 is too high an amplification setting. With the WAV, the AAR remains static on 64 quite happily. Why? The WAV was produced using RealOnePlayer, and the OGG using XMPlay and OGGENC.