Depends on how much you want to spend. For a quick and easy fix to my broken AS-6000 subwoofer I decided to attach a new sub amp externally. I got a second hand 150 watt plate amp on E-Bay but the Parts Express SA 240 for $99.00 would be plenty powerful. I then unscrewed the Athena amp and followed the wires to the sub speaker. Then I unhooked the speaker cables from the Athena amp and ran new 16 gauge
speaker wires from the Athena 12 incher out of the front port and screwed the old amp back in. That way I maintained the integrety of the sub box as I didn't have the time or skills to cut open an appropriate hole to fit the new amp. Next I joined the wiring to the new sub amp which will be an "external" amp, put the new amp beside the box, plugged in my subwoofer cable, plugged in the new amp, turned it on, ran some test tones and now have a reclaimed AS-6000 that sounds as good as new. Good luck with your project.