Check out rogerrussell.com for info on all Mac's older amps. Personally, you could do much better for the same money than the C504. To get balanced inputs, you will probably have to go to a C42, which is much more expensive. Earlier preamps had balanced outputs, but not balanced inputs. One preamp I especially liked was a C37, but again, it had no balanced inputs.
McIntosh Preamp Decision...C26 or C504
I've been using a C26 preamp for 30+ years. Now having minor problems. I don't know what aq C504 is YET, but I have the chance to buy one long distance from a friend. I don't have to pay for it unless I like it. He wants $750. for it. Is this a fair price? Is it an improvement over a C26? I would like more versatility. I would REALLY like it if it has balanced inputs. Any thoughts or opinions or advice?