I guess I can add a bit to Steve's impressions.
The stock CS4396/OPA2604 Zhaolu was nothing to write home about, to my ears. It was bass shy and lacked dynamics. Layed back, easy going tracks sounded fine, but when asked to groove, it was dull, boring, and lifeless.
The Zapfilter 2 brought it to a level I did not expect, based on my stock impressions. The bass was all there, tight and incredibly well controlled. My HF-1's have plenty of bass but it can be a bit flabby and uncontrolled. Not so with this DAC. It gave them a tightness to the bass I did not expect. Another thing it does really well is in the dynamics department. When asked to, it can really rock. The soundstage also improved dramaticly. Grados are not known for a large soundstage. With the Zapfilter the soundstage was wider, deeper, and more open, which was a nice surprise.
That's all for today,