I seriously looked into doing this too. There are some hi-quality 10 inch drivers made for the enclosure volume, including the SDX10, but they're slightly larger diameter. The Force opening can be enlarged to accommodate them, I wasn't sure if the feet would interfere with a router? Dremel has a router attachment that’s smaller than a standard router.
A blank metal panel cut to size with a RCA conn., volume control and grommet or Heyco clamp for the power cord. Something like a class d amplifier bolted to the inside of the panel would have lots of power.
I figured EQ could be done various ways, from an op amp type tone control internally, to any of the outboard devices. Graphic EQ, BFD, Velodyne, SVS, the box Mike used to sell and there’s others.
I thought it would be cool to have a pair of Force type subs, I really didn’t need another sub, or pair though. Christmas, the economy, etc. etc. I didn’t follow through.
You have an excellent enclosure, a little DIY and you’ll have a great pair of subs!