I've got music working using libmodplug. It needs quite a considerable amount of polishing up, and Ice M A N may come up with something better, but it's a start.

Using libmodplug means that, if you edit a level with JCS94, you'll be able to have background music in any of the following formats:
(Deep breath)
669, amf, ams, dbm, dmf, dsm, far, it, mdl, med, mod, mt2, mtm, okt, psm, ptm, s3m, stm, ult, umx, wav and xm.