Some of the best pre amps used for $600 or less

older CODA linestage

CJ PV10a

Perhaps a Dehavilland? They are underrated and underpriced!

I second the McCormack idea: I think you can get an ALD-1 for around that price. If you want to upgrade later, another $1300 through SMC Audio takes it to a level that few preamps under $10k can match.

good luck with your search!

Forgot to add the Eastern Electric Minimax. I sold mine for $590, and it was a great preamp, sounded awesome in my system.

I never thought of the DeHavillands as underated - underpriced? perhaps - but I think they are pretty highly regarded, certainly by those that have heard them.

You may want to try tubes to pair with your PS audio amp. The EE minimax mentioned earlier is pretty universally praised. You could also sell it off for little if any loss, I would think.

Every preamp on here is a winner in its own right and as stated earlier, not on any one piece, but most of these you could resell at a minimum loss if any. I suggest to buy one and start the hunt.