I would recommend experimenting with front placement some more before you buy another sub. Make sure you set the levels correctly and experiment with crossover setup. Also try different positions for sub in the front and see how it blends in.
The ceiling and front diffusers look very good. Do you have any before/after measurements? Does Rives target for specific improvements like RT60 with the treatments in place?
Would also be good to hear in your opinion what the areas of improvement are.
How much power are you feeding them?
I did this comparision a few months back and found that T8 held up very well except at near reference. I fed them approx 350 watts/ch. Not sure if that skewed the results.
Do you plan to use the T8 as surrounds?
Valid point about JTR. Since I was local, I auditioned the T8 and T12s in my HT for a few days before purchasing. Sometimes I wonder what the FR looks like for the t8s - subjectively I like them. The smaller companies like JTR and Seaton Sound will need to publish more information - specs/FR etc and get a few reviews (at least online) for wider acceptance.
Yes - I can easily distinguish different instruments with T8. I wouldnt call it depth though. Most speakers in this range do a decent job of "layering" - question is can they do it at high volumes. In case of T8s - they can upto almost ref levels.