Up2Stream 2.1 Amp with an active Subwoofer?

Hi there!

I am using a Up2Stream 2.1 Amp and running it with 2 passive stereo speakers fairly well.
Now I have an active Subwoofer and wanted to hook it up to the 2.1 Amp but on the small active subwoofer I have ( Fostex PM-SUBmini 2 ) only one Input for a non amplified signal.

Now the question:
Is there a way to use this subwoofer with the subwoofer canal of the 2.1 Amp. Maybe circumevent the amplification somehow or using the DAC Expension board as the .1 canal/subwoofer output configured with ACPWorkbench?!

I really don’t want to scrap the small sub because this thing is awesome and really fits my needs in a small room.

Thank you in advance!