Hi supernet
I've built the Velleman K4003 - its works great is is very cheap, all you need is a case and a transformer (50VA 12-0-12V).
Be aware that its rated at 2 x 10W into 8 ohms or 2 x 15W into 4, but that should be ample for your application. I say go for it.
Hope this helps,
Tim.