best pre-amp new or used for under $500?

If you are patient, you will find a Muse 3 @ $500.00. You won't find a Signature 3 at that price, but you won't find a better value than the Muse... Neutral, airy, nice slam and a remote to boot. Do your homework, read the reviews everywhere you can find.
I, like others can say, up your budget, but you'd be hard pressed to beat the Muse 3 for $800.00 to $1000.00 if what you are after is neutral and a remote.

This thread was not really started about DACs, but I thought I would relate the experience I had pushing music digitally through the Burr Brown 24/96 DACs in my Denon receiver. I dragged my old Toshiba HD-DVD player out of mothballs and used its optical output to pipe digital signal into the receiver, using a cheapo "redfish" plastic toslink cable from Best Buy (sacrilege on this forum?!?). Compared to my 15 year old Yamaha changer, all frequencies sound more extended and detailed. I can hear more of the music. Can't say too much about any improvement in imaging, I think the 685s trade that for neutrality. But anyways, a definite improvement.
We'll have to see what effect the loss of the changer has on my listening tendencies. The Yami changer has been boxed.

UPDATE - bought a Halo P3 last February, used on A'gon. Very happy with it.

UPDATE - bought a PS Audio DL III, running lossless AIFF into it from my PC laptop, Windows 7, iTunes--Pangea USB--MF Vlink--Wireworld COAX--DL III--Rotel RB-1080, sounds so good I'm probably selling the Halo...!

Audible Illusions....