If you just want to get a really good upgrade DAC (which will likely sound better than the Zappiti/Dune anyways), here's a short list at the $1k price point:
R2R resistor ladder dacs (generally more laid back sound, but more tonally thick/rich):
Audio-GD R-1
Denafrips Ares II (currently on sale at shenzhenaudio.com)
ESS saber dacs (more forward, detailed, exciting, revealing):
Audio-GD D-77 (with full clock upgrades)
Gustard DAC-X22
Other:
--USED-- PS AUDIO Stellar Gain Cell DAC currently on audiogon for $995.