Problems with wav files? I was playing wav files on my unaccelerated 500 with Play16 same as what you are doing. I would use my friend's Windows 95 machine to rip a CD to 8-bit 11kHz stereo wav, and play it with Play16. I played around with other sample rates for large wav files, but stuck mostly with 8-bit 11kHz since that was pretty much the best I could do with IFF files after conversion. Also did well for file size, about 1MB per minute, pretty comparable to what I would get from a 128kbps MP3.
Do you still have the version of Play16 you used? I have been trying to find a program that will play streaming WAV files from HDD/CF/SD on my A600, but the version of Play16 on Aminet is only for 020+.
I have already converted a bunch of my CDs to WAV files and I'd love to be able to listen to them through the A600, but at the moment nothing I have tried from Aminet will work. They work beautifully with Play16 and SongPlayer on the A1200 though.
As for playing MP3s on the 030, SongPlayer and Prayer are probably the best to use to get the highest quality and have nice GUIs and playlists. The biggest problem I've found isn't the quality settings, but the bitrate of some MP3s. 128-192kbps MP3s will play perfectly on low-medium quality settings, but you can forget about playing 320kbps MP3s at all, unless you decode them to RAW/WAV/8SVX first.
One thing that works well is AmiNetRadio, which can stream online radio and podcasts in real-time from the internet, playing at low quality on a 030, but it never skips a beat and continues to multitask with other Internet applications running.