fwiw, im using a bottlehead foreplay with my sim audio i-5 integrated. it has really smoothed out, in the best possible way, what the sim delivers. i believe the sim's strength is it's amp, not it's preamp, and the foreplay, as others here have said previously, is a real giant killer. just rolled in some amperex bugle boys and my gosh, what a beautiful sound. anyways, supposedley it's real easy to build, but im lazy and bought mine preassembled. i think there's at least one for sale here for a lot less than you want to spend. might be worth a try.
good luck!
good luck!