Hi Mike. As you know, you have almost the same amp/preamp combo as I did. I used a PS Audio Perfectwave DAC mk I with the VK-31SE/VK55 combo, and it was outstanding. I have since upgraded to the mk II DAC. You should be able to find a used Mk I in your price range, and you could upgrade the digital board to the MK II as I did sometine down the road. I don't think you can go wrong with the DAC IMHO.
Jim
Jim