Crackle/Fuzz Distortion with Gizmo 1.0M

Hi.

I recently purchased the Gizmo for use as an amp for my PC desktop setup. It's driving a pair of Energy CB-5s coupled with an Energy eXL:S8 subwoofer.

Now, for the most part it sounds great, except I can hear a bit of what I can only describe as a crackle or fuzzy distortion at certain times. I read through a few threads, and I'm wondering if it might be related to the issue with the voltage being input to the Gizmo? I'm feeding the Gizmo via my internal soundcard, an HT Omega Striker 7.1. I have no idea what the output voltage is with that card.

Is there any other cause I should be looking at? Should I look at some external DACs rather than using the internal soundcard?

Edit: Also, unrelated, it seems like the bass is a bit too loud. Unfortunately, on the eXL:S8, the input that bypasses the sub's internal crossover also bypasses the sub's volume control (weirdly), so I can't adjust the volume on the sub itself. The sub's crossover tops out at 100Hz, the same frequency the Gizmo's fixed crossover operates at, and I assume it would be sub-optimal to have two different crossover operating at the same frequency? Would the bass control on the Gizmo be a good way to address this? Should I just EQ it via software on the computer?