Might want to try out Not only is it one of the best audio players out there but is also a nice utility for conversion as well. It's basically like the modern version of winamp from the old days where there was plenty of plugin and third party development. [url=http://www.foobar2000.org/components]Here is list of addon components that expand functionality.
Specifically take a look the ADPCM decoders 1.9. That addon will allow direct playing/conversion of the sound format used by Sega in a lot of Dreamcast games (ADX).

Edit: I own the Dreamcast collection also. I ripped Sonic's theme - It Doesn't Matter from it to demonstrate.