Howdy,
I believe the idea of the "plane" applies to having a separate subwoofer, the sub built into the tower does not count.
The plane refers the distance of the enclosures from the listener. So you would not want your subwoofer placed next to your tower but sitting a foot closer (or back) from the listener. From what I understand you would want to apply the same idea to your tv, keep the big screen even distance as the speakers from the viewer.
I may have read somewhere this has to do with defraction effects.
Perhaps someone from Aperion can weigh in...
-James