Hello!  I'm a longtime fan of Head-Fi.  I've used your reviews and insight to setup a pretty sweet audio experience for my PC and home theater, but I've run into a snag with my sound card.  I have the HT Omega Claro XT model ( http://www.htomega.com/clarohalo_xt.html )
 
The issue I've been having is when I'm gaming with my headset.  My system's audio bleeds into my microphone terribly, causing some echo if I'm in voip applications like ventrilo, teamspeak, etc.
 
Checking the cards documentation ( http://www.htomega.com/filedown/halo0818.pdf ) page 6 mentions the MIC IN has a special opamp that increases the MIC input gain.  Page 10 shows the headphone impedance jumper as well as the 4 swappable opamp.
 
I've tested 2 headsets, the Sennheiser PC350SE and Sennheiser PC360 with the HT Omega and a cheap little usb sound card ( http://www.amazon.com/gp/product/B001MSS6CS/ ).  The leaking is only coming through on my HT Omega.  The Syba card would be my solution, but the HT Omega's Dolby Headphone sounds too good to part with.  I'm writing to ask what my options are.  Does this sound like the headphone impedance jumper issue, or do I need to start swapping out opamps?  If it's the latter, I'm not sure where to start with that.  The card sounds fine, which is why I haven't really tinkered with it much.  My priority is to keep a great sound, but eliminate the MIC IN gain.  At this point I'm only guessing that's the culprit.  So I turn to the guru's for help.  Thanks a bunch for reading and any assistance you may provide.
 
EDIT:
I forgot to mention I've tried both the official HT Omega drivers and the UNi Xonar drivers.  Neither one fixed the issue.