Sometimes you can cause a hiss on either left or right channel, or both. You can usually make it disappear by playing random data, however this might not be a very nice thing to your audio equipment, but it is the only way I have found out to be effective.
Only the Codec is used in this version of the driver, therefore only 2 channels are supported (left and right). Also sound quality is probably worse at lower kHz compared to playing through the synthesizer which does interpolation.
If the implementation has a 'bad' oscillator, using frequencies 44.8kHz and 38.4kHz will result in incorrect playback frequency. The author has a GUS PnP Pro which displays this behavior.
Other members of the Interwave family have not been tested and don't have the glue needed to make them work. Should someone need to implement it, not many changes in the existing code are needed. Output voltage control in register CFIG2 [7] should be set differently for some other members of the family.
Other architectures than i386 haven't been tested. The bus_space abstraction has been used from the beginning, so it should work.