DAC 3-4k range

The Berkely, Lamp, and ARC would all be high on the list to try. Possibly the AMR.

A DAC with built in volume control could be nice, since my next logical upgrade may be a separate amp but a significant obstacle to that is the need for an expensive pre.

Will you be upgrading the 2.1 that you have to a 4.1? or will you be selling the 2.1 and buying a whole new unit?

I was listening to a lampizator 3 tonight with the volume control option driving an Alchemist Forsetti Signature on a pair of Daedalus Ulysses speakers and it was very competent in the volume control position. The system wasn't lacking in the ways I feel a system usually does in the absence of an active preamplifier.

That said the system was employing a lampizator transport which was not cheap.

A great thing about the used equipment market is it can allow you to try lots of things in your own system, and if it doesn't work out you can turn around and sell it for little or maybe even no loss (assuming you don't overpay for the unit initially). And DACs in particular are relatively light and have no moving parts so lend themselves well to shipping. Comparing your unit to others in completely different rooms/systems or to lower-priced competition really doesn't tell you much imho. Anyway, just a thought. By the way, I'll throw in the Bel Canto DAC3.5VB as another unit worth exploring if it hasn't already been mentioned. I had the DAC3VB in my system as a demo and it was very impressive (would still have it if I could've afforded it dammit). Again, best of luck.

i am surprised no one has mentioned the minimax plus dac. i would also suggest removing the op amps and substituting the dexa opamps, based upon my conversation with the importer.