I was very surprised to see the amp controls on the sub, they are nothing like the photos on catalog sheet here online. The photo shows a switch for 0 or 180 phase. But what i got was a full range pot from 0 to 180 degrees, so you can adjust anywhere in that range. I found 45 degrees sync'd up best for a harmonious sound with the Model T's and with more apparent felt output.
So you say that the XLR is of course more immune to noise pickups as it is balanced, but also less signal degradation? I guess that's what I proved out, yes a huge improvement in detail and very apparent tighter bass response, it was immediately evident.
For my installation, the 150 hz crossover is more dynamic; it melds best with the Brystons.
When you get your 800, let me know if the amp has the full range pot for the phasing vs. the switch.