Do the *.dspw files play in VGMstream? I'm assuming that they do. If yes, then open the command prompt, and run VGMstream (aka, "test.exe") using || FOR %a IN (*.dspw) DO test -l 2 -f 10 -o "%a.wav" "%a" || (remove the spaces at the beginning and ending of that statement...). Essentially, this will output WAV files, which loop twice, and have a 10 second fade.
As an extended explanation (in case the above was simplified too much), you can check here and here. Note that the former is as thorough as I know how to make it (the person I made the instructions for didn't speak English, and had no concept of what the command prompt was, at all...). Thus, more than likely, you'll be able to skim/skip most of it. The important difference would be, instead of "*.xa", you'd use "*.dspw".
As for the second link, it explains some of the parameters available to VGMstream, so you might want to check that (I talk about looping, fading, file names, etc.). It also mentions how to put all of this into a *.BAT file, which can make it even easier. With a batch file, you won't need to deal with the command prompt at all. Just make sure that all the necessary files are in the right directory, and double-click the *.BAT file, and if you have it set up properly, the directory should start filling up with WAV files.
Once you have the WAV files, use any MP3/OGG/FLAC/APE conversion program you want. Personally, I use oggdrop or lamedrop, but you're welcome to use any of the innumerable tools out there.
Hopefully this has been helpful. Also, hopefully VGMstream can play *.dspw files (I'd be very surprised if it can't, considering it's using the DSP extension, more or less). Good luck! Mouser X over and out.