Great results, very impressive. I am getting a 2nd sub myself so it is all ahead of me
Are you using Audyssey in the end or there is no need for it?
Yes definitely using Audyssey.
The process ended up being:
1) Turn off Audyssey. Use recommended settings on each Sub (in this case for the Arendal 1961 1s's this was Ref Setting, -6db Input Gain, Number of Subs 2).
2) Use REW and MiniDsp 2x4HD to time align Subs by testing at various delays. Looking for flattest line and highest combined output (measuring both Subs but using a delay of 0.25ms increments - first Sub 1 then Sub 2). Ended up using Sub 2 delay of 2.5ms. From that point on the Subs are time aligned and should be treated as one Sub to the AVR.
3) Reset AVR Crossovers on all speakers bar Subs to recommended XO's. On mine this should be 80Hz but 100Hz is actually better. Then with this done, run Audyssey.
4) With Audyssey on, use REW to look at L,C,R without Subs, Subs only (by running a left sweep with left main disconnected).
5) Further adjust AVR Sub Distance (timing) to align with mains (turns out a reduction of 90cm was best).
6) Run sweeps of L+Subs, R+Subs, C+Subs, and then adjust Sub levels with a REW created PEQ Filter added to MiniDsp Input 1 (which Subs are connected to Output 1 and 2).
@mb3195 found that the Subs were actually running 6db to low, so this may be because the Arendal recommended setup (without MiniDsp using Denon/Audyssey) is -6db, which we had set. Suspect the MiniDsp didn't help here. So I reset both Subs on their settings (not on the AVR) to 0db Input Gain back up from -6db Input Gain.
Have also added a further 3db uplift on the AVR for taste
. Now I'd like to say I knew how all this was actually done but what we actually looked at for 5) and 6) to get there is a mystery