Phil, what are you trying to control with the M-Audio? I assume it's a softsynth, but try to avoid using the Microsoft GS synth. It has a fixed latency of about 350 ms, no matter what your latency setting is. I suggest using Cakewalk's included TTS-1 synth as it has better latency performance. (For you Cubase users out there, try to look for the Universal Sound Module (usm.dll) in your Cubase directories. I think there is an option to install it when Cubase asks you to install Cubase 5 plugs.)
I generally prefer to use asio drivers with Sonar as I get better latency figures with it. Insert the TTS-1 into the Instrument Rack in Sonar and adjust your latency until you can play it without audio breaking up. I've found 5 - 10 ms to be very unnoticeable (I can go as low as 2 ms but cpu usage increases).
One of the reasons I've retained my midi modules and synths is because of latency, though I'm increasingly finding myself going virtual with my sounds during mixdown. It's still sometimes easier to noodle around on a keyboard while recording it's midi output then fleshing out the ideas when the creative phase passes. I thought you were going to get that Roland G-70 workstation, Phil?
@supacow - You can use the M-Audio controller on a Mac. There are downloadable OS9 and OSX drivers. Some USB controllers and audio interfaces are so completely compliant with the USB spec that they don't need drivers and the OS readily recognizes them (not all devices but there are a few out there).