See if you can find a used Tampa (M-Audio). It's got S/PDIF out, and I've been getting some nice results with it. It has a compressor and EQ also, and I love the variable input impedance selector. I paid $270 for an as new one.
ART DPSII
ART Digital MPA
Samson (somthing or another, its mono, but has a in to chain another pre to its a/d converter to have a stereo out, BUT, you are locked to 48K or 96K)
If you could locate a used ART DI/O converter (they are no longer made) you could use it with whatever preamp you want. I have a couple of these and they sound surprisingly good for the money.