Mid-priced warm sounding DAC?


I've recently decided that a good route for me to take is upgrading my system with a good DAC. My current system is a bit bright sounding, so I'm looking for a good DAC costing up to $600 (used) that will provide a smooth, warm sound to match my currently bright system. I'd also like the DAC to be capable of upsampling, although if necessary I could add an upsampler to the digital chain at a later time. My preference would be to have it built-in, however.

Any suggestions?
jwglista
Thanks again to everyone who has offered help and suggestions. The Audio Mirror looks pretty attractive; I’ve been reading good things about it.

Well, my system has been built on a low budget. I know that there are a few elements that are responsible for some of the brightness. My amp is an NAD C 340 integrated, and currently I'm using an NAD T 532 DVD player for CDs, and a Sony DVP-NC685V for SACDs. The NAD sounds MUCH better on CDs than the Sony does, but it belongs to my dad and he'll want it back in a few weeks. After which, I'm back to the Sony and another cheap Philips CD player that I have (CDC-751, actually sounds better for redbook CDs than the Sony). My speakers are a pair of Triangle Antal XS, which are the culprit of the bright sound. I've heard that these speakers go very nice with tubes, so I'm thinking that a tube DAC may be able to level out the high end. The speakers are toed in, and the manual states this is the best way to have them. The speakers are firing long ways across the room, and I have some blankets up on the walls to help with standing waves. The room is about 13' x 16', a medium-sized bedroom.

Either way, I think upgrading the DAC will be a huge improvement. Right now I'm using QED silver anniversary biwire speaker cables, but those will need to be returned eventually also. I'm using Acoustic Research Master Series interconnects. Any suggestions on cables or anything else to help improve the sound?
All speakers sound brighter when toed-in. Point the Triangles straight ahead and see if the tonal balance becomes more even. Soundstage should also seem wider and more expansive, though images larger and a bit less precise.
I had Triangle Celiuses and they were kind of bright sounding. Replaced them with Merlins and havent looked back.
I read here: http://www4.head-fi.org/forums/showthread.php?t=134464

that the unit from PothAudio is basically the same unit as the Audio Mirror D1 NOS DAC with nothing substantively different. Can anyone who has heard the unit confirm this? The price is right...
There was a thread here recently that was removed regarding the similarities between the Poth and Audio Mirror. The owner of Audio Mirror posted a response similar to what was said on the head-fi thread. I have two of the Audio Mirror units, one that has been modified by TRL. In comparison to the Poth, to the eye they seem very similar, with the obvious exception that the Audio Mirror uses the teflon caps (which according to TRL are very good). The owner of Audio Mirror has told me of other changes that he made to the circuit, but I'm not an engineer so I don't know for sure. However, one way to know for sure is to compare both of them side by side, which will also allow you to A/B for sound quality comparison. I'm ordering a Poth for that precise purpose. To my knowledge I have heard of no direct comparisons between the two products from anyone that owns both units or has heard them together.