Greets!

Yeah, the 515's extra 'snap' comes through even when XO'd at 500 Hz if HF loading caps are used. My room has no real gain to speak of, but a second 515 in a large enough cab fills in nicely, so assuming your room's construction is rigid/massive enough to get good corner gain (~ +6 dB of a theoretical +9 dB available), a corner cab tuned down around Fs should do well enough.

Note that a room's corner gain curve basically boosts much/all of the cab's BW to a greater or lesser extent, so to flatten it in room usually requires some EQ (often handled by the XO inductor's Dcr or additional series resistance), but always better to attenuate rather than boost.

Hadn't worked out its ~net Vb, but if it's this large, then it's not that far off from my ~10 ft^3 net/driver, so with the 515 up top and a 6" dia. x 6" long pipe or equivalent shelf vent down low ought to get you there with longer being required with shrinking net Vb.

One of the reasons I wanted to get at least one of these cabs is to find out if my preferred PL construction adhesive will work on whatever thin veneer/wallpaper lines its innards without pulling it free from the substrate or flat out melting it since the reason for using it is that I can run a thick bead on a board's edge, push it into place, wiggle it around to spread it/work out any voids and forget about it. For cross tie braces, I add a drywall screw to hold its ends in place to the ridge boards once they've set.

IIRC, Liquid Nails is ~the same product, so if you want to be the Guinea pig........

GM