I am upgrading from Audiotrak Prodigy HD2 to Asus Xonar Essence STX. Prodigy HD2 is great soundcard, but only for PCI and it needs 12 W on 5VSB rail from PSU (and I am moving to new low-power PC with PSU only with 10 W 5VSB). But before that, I am testing both soundcards in my old PC, with Pioneer A-30 amp and Wharfedale 9.2 speakers.
Sound from Essence is pretty good, but I hear some weird thing - sound "pumps" in strange way. It is very hard to hear, but it is like move volume up and down little bit and very fast. It is mostly hearable with brown noise test sound.
I appreciate very much, if someone could test it for me on his STX. Here is that sound: http://www.audiocheck.net/testtones_brownnoise.php
On Prodigy, brown noise sound is pretty still and straigthwards, no pumping at all.
Tried also some opamps swaps (LME49720), but problem on STX persists.