Independent Subwoofer Setup Question

I have been running two subwoofers connected to my Marantz processor using the Audyssey Pro room correction. I was checking out Marantz’s new AV10 processor and they were making a big deal about their 4 independent subwoofer out improvement for directing bass. You can designate where in the room a sub is located and the processor will direct bass for the corresponding channel to that sub. I said I can do that now with my current setup. Bought a Martin Logan Forte 2 channel amp with a sub out for my rear surrounds. I connected the sub in the back of my room to the Forte, ran ARC room correction and setup my processor for running a single sub. I didn’t know if it would sound better or worse so I have been auditioning with movies and music.

It sounds better, MUCH better. It feels like the room is pressurized more evenly from front to back and I don’t feel I lost any of the bass I had previously. I like it.

My question, I am going to add a third sub using the same method to the amp driving my rear atmos speakers. What type of sub should I use (wall mount, ceiling mount. or box) and what sub should I purchase? Thanks.