Actually, all the TrikToys amp consists of is a small amplifier from Radio Shack that costs under $20, two 20mm model train speakers, and a powered headset mic.
I made my own, and if you guys want I can take pictures and dig up the parts numbers to help you build your own, but it's not super loud and you have to change the watch battery in the mic after almost every troop.
But I will say that his mic tips are pretty nice.