That amp is only 45 watts at 8 ohm, so it is a little light on power.
This one would do the job for only a few bucks more, and might even fit into the cabinet. Information as to highpass and all that is pretty light though. Looks like a 25 Hz highpass with 3 dB of boost at 40 Hz. Not a bad fit, might actually help things to be honest.
Depending on what you're after - an old-school stereo receiver can be a fine amp for these - all you need is 100 W into 8 ohms. I've scored some good stuff at the local thrift stores.
You could maybe even run these off the extra channels in a 7.1 receiver if you only run it as a 5.1 and the receiver has preamp inputs like mine does.
Would mounting that Apex Jr C-6 into the back of the cabinet ruin the tuning?
I built a pair of these subs but the output was just not enough. I can see how with four it may be great but I don't have the room for them. I also found that they were easily pushed to much and would get "funky" but that's on me.
I will say that I ripped out the drivers and put them in some 0.5ft^3 cabs tuned to 45hz and they rock! So I would caution anyone looking for medium to high output. That said they would make a great computer sub sitting next to a desk.