Custom Line Thunder 99 : Great little unit but problems with the headphone output

I bought this pedal/power amp to boost my overall guitar volume and run 2 speaker cabinets at the same time (2x50W out is LOUD!). I play in a hardcore punk band with minimal effects. I have 2 stacked distortion pedals running into an Orange Terror Stamp which is being used as a preamp. I then connect the line out of the Orange to the input on the Thunder 99. It does not color the tone at all and just provides more volume to the speakers. This is exactly what I was looking for. 1 issue: - The headphone jack has a problem where audio is clipping no matter what I use for headphones or inputs to the pedal. Since my Orange Terror Stamp has a headphone out this isn't super important to me but it would have been nice to have the unit fully functional out of the box as it is not a used pedal and I did pay full price for it plus international shipping to the US.