Advice

Nk - The best transformer on the planet is the Finemet from Japan. I use these in my Final Drive buffer:

http://www.audiocircle.com/index.php?topic=108715.0

You can find these for DACs on ebay. They are about $1K

Next to these, maybe the Music First.

Steve N.
Empirical Audio

A lot better IMO. If you reduced the jitter of the source by using a quality USB converter and a good power supply. Also you could also eliminate a ground-loop by adding a good 1:1 signal transformer between the DAC and the integrated amp.

Beyond that, you would have to change out the DAC.

Steve N.
Empirical Audio