I'm using a VERY simple setup. Throat-mic, with push-to-talk, and an amplifier.
Basically, the speaker with amp is from an PA system commonly used by guides, so it's loud enough. The throat-mic helps with making it easier to take the helmet on/off. Now the key is the PTT button. Whenever I press it to talk, you hear a distinct click in the speaker. Likewise when I let go of it after speaking. So I have no need for costly FX-cards...
Actually, it sounds so good, that alot of other garrison members have started using the same setup!