I'm pretty new to this and would like some advice from those of you who have experience with external USB audio interface cards. I've been researching multiple devices and can't decide on a specific one. It would mainly be used for classical/operatic type vocals. I have a Sennheiser MD432 II Dynamic mic that was purchased about 8 years ago and see that it is still being sold and has good reviews - so I probably won't need another one, although a condensor might be better suited for my needs. A few of the cards I am trying to decide between are: M-Audio fast track pro, Edirol UA-101, Native Instruments audio Kontrol 1, and Digidesign mbox 2 pro. I'd like to spend less than $600 if possible. Any advice, tips, or suggestions on which of these or any other USB audio interface cards would be best for classical/operatic vocals would be greatly appreciated. PC is a core 2 duo 2.4ghz, 4 gigs ram, Vista. Thanks!