I'm pretty sure the baffle is 1.5" thick and the rest is 3/4" or 1" MDF on the UREIs. The E-145 has that thick frame that is counter sunk into the baffle 1 layer of the MDF. The subs are 1" MDF following the Greg Timbers plan in the library.
I think your description of the bass as dry is a good one. That's what I meant when I said no overhang. Snappy transients and quick start/stop of the drivers. I had several drummers and bass players here who thought the bass articulation was excellent. I think a lot of listeners probably prefer more bass bloom, but that's just a listening preference. The fill is super easy to remove if you want to experiment but you can probably change/adjust the mid-bass more effectively (if you want change) by rotating the cabinets to put the helper woofers closer to the side walls.
I'll see if I can find the folks I bought the wool from (in Canada I know) but you probably won't gain anything in the 811s as the single E-145 isn't playing much bass in that size cabinet. You're going to want subwoofers under them for sure and could probably tighten the subs up by adding wool depending on what type you use.
As always, the room will likely have more influence on the bass response than does port tuning and positioning. I had a good room for bass response that helped a lot. I have an engineer friend who always says after a failed audio experiment like trying out a great speaker in a bad room, "Once again, beautiful theory butts up against ugly old reality".
JBL was going to find a way to sell studios control room monitors and there's no better way than buying the competition (UREI) and offering that product as well as a slightly different sound with a very different look. :-D