I've plugged in my $150 mic and it doesn't work. (Mac and PC)
The iMic was configured for Mic and Line Level devices, such as standard computer microphones and tape decks. Those devices (and there are many types) typically are high impedance products that connect via unbalanced cables. Many, if not most, professional or higher end microphones are low impedance products that connect via balanced cables. Those types of devices require preamplification to bring them up to Line Level. This can be accomplished by using the pre-amps of mixing consoles or by using an impedance matching transformer. If you don't have a mixer, the transformers are readily available at electronic supply houses and consumer outlets such as Radio Shack.