First of all I sent you the wrong driver link. This happened because I have the wrong link on page describing the in wall system. Sorry about that.
This is the driver you need.
These are the build pictures of the speaker.
The plan is below.
Now what you will need to do is put the driver on the adjacent face by turning it 90 degrees. The internal depth of the cabinet is 12"". Now you may want to widen that dimension to make room for the driver on that different face. This you can do.
Pipe length Pl is 3'
The taper is 3:1.
The pipe volume Vp is 120 liters. So it is about a 4.25 cu.ft enclosure.
The beginning of he pipe (closed end) is 600 sq. cm.
The exit area (open end) is 250 sq.cm.
Stuff with polyfill from Walmart. The weight should be 960 GM, about a KG, which is 2.25 pound near enough. Distribute it evenly throughout the pipe, but keep it a little short of the exit. I staple netting around it to stop it settling. I do not use glue as it hardens the polyfill. I do not directly staple the polyfill as it compresses it.
That makes for an impressive and excellent sounding bass system. You can mount the mid and tweeter above the woofer. This maintains excellent output to 20 Hz.
I don't think you will need a sub. Since you are biamping you can blend in the LFE signal with the low pass output from your crossover.
