Just wanted to note that I got a 583s and while it wasn't cheap (had to sell some stuff I liked to get it), it's totally worth it-- a great, huge, smooth sounding tube preamp. I tracked down a 50's square getter, longplate Mullard 12AX7 and a pair of 50's Raytheon Blackplate 12AX7s on Scott's recommendations only to find that my unit (a PotLuck Con demo) came with a nice Fisher 12AX7 already installed! Even still, I put the Mullard right in there and am very pleased with the sound. I've only tried vocals with it, but that will be my main use anyway (along with acoustic guitar). I'm looking forward to trying the DI with it for bass and electric guitar though.
The build quality is excellent and the LED switches are very cool and helpful. This isn't a "toob" preamp-- the tube runs at the proper voltage thanks to Scott's rather ingenious circuit.
I'd definitely recommend this to any of the few, but mighty 500 enthusiasts here on Home Rec.