The Musical fidelity amp is killer for the used price. If you like the 545 sound you'll love the MF amp and preamp. I agree that the preamp is as important as the amp, when funding allows I would upgrade both to MF gear. If you don't need the extra power I would avoid the Adcom 555 like the plague, the 545 sounds so much better from top to bottom, but on power hungry speakers it does clip easily....