I just bought a Helix LT, and I'm having issues trying to use Helix as an interface. I'm sending the XLR out as a line level to my Rokit 5's, and also sending my USB to my computer. When any audio signal comes out of my computer, through the helix, and out to the Rokit 5's, there's a bunch of crackling and popping. I have the volume set quite low, I've isolated the helix, computer, and monitors each to their own outlet, I've changed the USB cable around to various USB ports on my computer. It happens if I playback stuff I've recorded in Reaper, when I watch anything on YouTube, and during normal system sounds, but it doesn't happen at all when I'm just using the speakers to directly monitor the Helix.
On a side note, does anyone else find that any signals sent through the USB are really low? My amp is set to 10 on the channel and master, and 5 on the drive, and the signal is incredibly weak compared to the signals coming out of the computer.