PS.
I enjoyed my REL T/9x paired side-by-side with Harbeth 30.2 XD. For that application (simple bass extension) variable phase wasn't necessary.
In my current application, I needed to deal with nulls and asymmetry in a listening space that opened up into a large open plan living space, as well as pressurize that space, which meant placing the subs behind the main listening position.
In this case variable phase adjustment & multi-band EQ was absolutely necessary.

