Near as I can tell you should be seeing a few different sets of options, from the manual I am seeing S/PDIF on RCA or optical, RCA aux ins and a 1/4" mic/line in with a knob for adjusting the gain. Let me know if I've got the right documentation, which input you are using, and if you are using the 1/4" in where you have that knob at.
I'm sure we can get something working for you, I was able to get something out of a much less capable card from the same company some time ago.
I'm using the 1/4" line-in. I've got the gain knob set just barely on. I pretty much turn it til it clicks "off" and then turn it back until it's just above that. Turning it up from there obviously makes it louder, but in both cases there seems to be about the same amount of distortion, it's just easier to hear at higher volume.
I've also considered the cables I'm using. I've tried going from the DI to the 1/4" line-in with a male-male 1/8"jack cable adapted to 1/4" at both ends. I've also just used a 1/4" to 1/4" audio patch cable, straight from the DI into the 1/4" line-in.
