Mr. RC sound Pro - B Sound System
I purchased this, but it won't fit in my plane. Sounds really cool with engine and machine gun/cannon sounds. I't brand new, I still have the original parts and accessories. My loss is your gain. I paid $160 shipped for it. $125 shipped USPS priority mail.
This has the Lycoming, Pratt & Whitney Double Wasp, Wright Cyclone and BMW engine sounds. As well as machine gun and cannon sound.
Here is a nice review of it...