Cool pics, nice space and I love all the natural light.
I really dig seeing various types of normal, non-dedicated rooms, and the manner in which they're used for audio.
Also, this entire idea, the floor joist horn sub, is so cool and unique. The exit being where it is is fascinating as well, reminds me of the mammoth under-floor
horn sub that Italian dude built. Anyway, I'm interested in your impressions with playback.
Just a friendly suggestion, with my previous set-up config, I had all three LCRs across the front, above my 60" display, all at the same height and toed in and angled down to the primary LP. This placed them up closer to the ceiling, just about the same height as your center. The energy reflected easily smears details, in a frequency dependent manner.
Oftentimes, the ceiling isn't considered for treatment, and simple panels can help significantly. With my LCRs, their performance was very much improved with a single absorption panel placed at the reflection point in front of each one of them. This really helped clarity, with zero negative impact to immersiveness/spaciousness (that may occur with excessive sidewall treatment).
Due to the proximity of theceiling, and since the angle is so slight, grazing angle and overall effectiveness need some consideration. A simple trick I did was move the panel a little farther away so a good bit of the MF/HF energy "sees" the panel edge as well as the main bottom side.
Sorry for the OT,but I've removed and reinstalled my absorption treatments so much, in various experimentation and measuring. Their impact never ceases to amaze me.
Thanks for the update and sharing the pics, I was wondering whatever became of this.