I hate to see a hanging question.
I played with one like this, you should be able to find a couple of them less expensive if you look around:
https://www.ebay.co.uk/itm/DC12-24v...=item4423f63624:g:JswAAOSwhilbXubZ:rk:41:pf:0
This specific board has its own crossover dial, and it worked well when I tried it.
Realistically expect <60W per board at 24V, without distortion setting in,
But they work well, TPA3116 make for decent low power sub amps. This board convinced me that subs are compulsory rather than optional..
You could still use an external crossover if you turn the crossover dials up to maximum.
Alernatively you can use a standard 3116 board but you want one that can be set to mono by bridging the two channels (called BTL or bridge tied load).