Just checked my line-out with my Klipsch Promedia 2.1, no channel imbalance in mine. I'd do a little more testing with a second system if possible to make sure it's not an issue with your speakers, then reach out to HRT once you feel certain there's a real problem, I'm sure they'll be glad to help.
I tried the exact same thing, put my K550 headphones in the line-out. There is music in the left phone while the right one only distorts, there is no audible music at all. I think my mS is broken, I'll send a mail to HRT and talk to the retailer tomorrow.
Thanks for the input! :)