there is one setting which says "properties for" when I changed it to M-Audio the format was set to 48000hk...so I switched it to 44.1
is that I should have done?
Yes, that's the place, and keep an eye there to determine how well the M-Audio software and drivers for the Transit are functioning--and for many of us, releasing timely drivers isn't where M-Audio distinguishes itself. You'll want digital out/AC-3 passthrough with a dvd, and ideally when you switch away to iTunes it'll just seamlessly (and transparently) switch to 44.1 within both Audio MIDI and the M-Audio control panel. Keep both in your dock for a while so you can check quickly.
wouldn't hesitate upgrading to something else if it made a difference playing back music.
See how well the Transit does for you first--if the Transit isn't forcing everything to 48 you'll be ahead of the game. I still have my M-Audio Firewire Solo connected to a G4 PowerMac (originally I got it to complement a G4 mini) and with Tiger drivers the Solo was always rock solid--handling iTunes, AC-3 passthrough for dvd, and even digital out for high def EyeTV recordings. M-Audio hasn't exactly been proactive transitioning their devices to Leopard--in 7 months the best they can do for some models is a beta which breaks the AC-3 pass through functionality--the very reason most Mac users bought them in the first place.
Granted music is your primary focus, but if you also rely on your mini for any other home theater function besides music, you'd probably be much better off stepping up to any Intel Mac, which all have built-in optical out, rather than rolling the dice with another M-Audio. However, if you plan to keep the G4 for a while, and keep it mainly music oriented, then there are plenty of other USB and firewire DAC options you can choose besides M-Audio--its uniqueness and value was solely the true AC-3 pass through for Apple dvdplayer.