The X991 has the following "distance" settings on both DTA & POSITION:
0.00, 0.17, 0.33, 0.50, 0.67, 0.83, 1.00, 1.17, 1.33, 1.50, 1.67, 1.83, 2.00, 2.17, 2.33, 2.50, 2.67, 2.83, 3.00, 3.17, 3.33
On the DTA setting you can adjust FRONT, REAR and SUB (the front & rear do both left & right the same amount at the same time...the sub has only 1 channel and adjusts it away from you).
On the POSITION setting you can adjust FRONT, REAR & SUB (all 3 of these have independent adjustments for EACH side...unlike the DTA setting which adjusts both sides at the same time).
The way I have mine set (I'm always playing with it so it varies a little from time to time) is that I use the DTA feature to set the distance from my CLOSEST speaker to my head (say 0.67 feet)...this will make BOTH left & right at 0.67...I then go to the POSITION setting and I leave the left front @ 0.00 and set the right front and the difference between the 0.67 I used in DTA with what distance it really is (say 1.83 feet)...I then do the same type of thing for the subs.
There are some days where it doesn't sound like the front stage is perfectly balanced so I play with the numbers a little to get it to sound balanced...the subs I rarely ever change because it doesn't seem to matter that much.
Hope this helps a little...if not maybe we can meet somewhere and I can show you in person what it does (since we don't live too far apart).