Brendo, you dont need to have your subs placed the same distance to your mains, but you would need to be able to delay (advance them stricktly speaking) them independently to align them properly. The newer Denons allow different settings for delay and trim for 2 subwoofers for example. You are really only able to do this for one point in space, and over a narrow band when aligning to mains.
Without independent delay the subs can be aligned to eachother physically by placing them equidistant to your position AND the mains. Otherwise cancellation with one channel or another. Symmetrical setup is really the best to deal with this.
The newer subs probably have less lag than my older svs subs. It would be interesting to see how the Axiom subs behave. It wouldn't surprise me if they were a little better, but probably all powered subs are 20ms or so behind their smaller passive speaker counterparts. If your AVR auto cal sets the sub distance wierd (long) this is likely whats its trying to correct for.
