RGB, just about any Amiga mod player will run on your CD32. EaglePlayer, HippoPlayer and DeliPlayer are probably the best ones to start with and should play just about any mod format with their various plugins and engines. Personally I prefer EaglePlayer for its GUI, and it plays all the mods I listen to.
Keep in mind that the CD32 has a pretty weak power supply which wasn't intended to power motorized expansions like hard drives, which is why many of us stick to using Compact Flash cards instead of hard drives these days. If you intend on keeping the hard drive, you might be best to get yourself a small ATX PSU and use an adapter like the one from Amiga Maniac, which will provide plenty of juice for anything else you want to add (like four daisy-chained floppy drives and a video digitiser, if you felt like it). You can get them here http://www.amigamaniac.com/atx_to_amiga.html