I have two 557s and have been considering selling one of them but can't quite bring myself to do it. That said, are you sure yours is completely dead? One of mine was also pronounced dead but I found a very talented bloke in Croydon who rebuilt it and it's now better than ever. It wasn't cheap but was no more than a good second hand 557. I guess it depends on the magnitude of the fault in yours?

System: DSP7200SE (upgraded) + RPI (PiCorePlayer) with Allo Digione running Squeezebox system.

Also various legacy 500 components - 557x2, 502, 508-20bit, 566-24bit plus too many other misc amps/speakers.