It is applied to the channels. So both front-left and rear-left speakerts will be delayed if you delay the left channel. I think it was discussed before that fron-rear delaying is not currently possible from the empeg sw, since it only outputs left and right (2 channels) and not front-left, rear-left, front-right, rear-right (4 channels). It's a hardware "problem", not a software one.
I have to say, though, that with just the current function my car installation sounds amazingly well... I honestly do not know whether I would need and benefit from anything like front/rear delay. I'm just assuming, now, I admint I should at least try. The fact is that I could HEAR the problem with my stereo image before the current patch was made. Now it does seem perfect, I do not hear any problem.
Ehm... Ok, I just realized I do NOT have rear speakers, just a sub. Ok, I'll go to lunch. You guys stop laughing...