Could be. The Original FW was never intended for that player. HDMS probably had too much output V for the input of your amp. Should have just used the volume control.
That said, you may still be able to re-install the DT FW. The SOC is hard to brick though you may have pulled it off. Hit the reset. Hold the up and only the up button while connecting to your PC and wait 10 seconds before releasing it. Start the DT updater and see if it discovers the unit. If it does, I'd format it before beginning the update process. Good luck. If that doesn't work you'll need to contact Jack as they'll have to flash it at the factory.