If you're talkin about Xonar HDAV, you don't need anothr DAC.
On Xonar HDAV1.3, it already has amazing analog output (BB1796 DAC + NS LM4562 OP), which is the dreaming combination of many hi-end users.
In fact, it might be even better then lots of the mid end AVR DAC sections or stand alone DACs.
If you really want the best, go with Xonar Essence STX it's a stereo output only sound card with BB1792+ LM4562.
It's not just the componens, Asus has really fine tuned...