Hi....Can't figure out this one. I have a 1.42g power mac. I use Garageband for voiceover work. I've got an Electrovoice RE-20 plugged into an M-Audio Firewire 410. I almost have to turn the gain up full to get a good voice level. It's neither the cable nor the mic (I've tried other mics too) that's the problem. I've checked them both. Turning the gain up high, causes, of course, a lot of hiss. The 410 is set as my audio in and out in the preferences, but when I run the output through the 410 I have a loud hiss. When I run the audio through the mac, I don't get as much hiss. But I always get hiss from the mic input. What could this be? My audio work demands a clean signal. The hiss is killing me!

Are you running the mic directly into the M audio interface?
If you are you may want to try a pre amp. Check out the Focusrite trakmaster its not that expensive. It will help you bring up your levels and also give you a nice sounding mic.