I’ve had the same experience. Once I forgot the subwoofer was hooked up when a friend wanted to "see how loud it can get". In my case they suggested that I just buy the newest modular amp at a very reasonable price getting an upgrade to a newer version for not much more than I would spend on the repair. It was plug and play.
Great service from HSU Research
Just FYI, my old HSU sub needed servicing. I emailed HSU (Steve) and got a quick response back, agreed to sent them just the amp itself and it was fixed and back in my hands in a week or so. Very fair price too. Good job HSU!