QUOTE (Reza)
Say i have two same subs and i run them with two different brand amp, that wouldn't make any difference??
Different question, actually.
Yes there could be a difference, the power levels between them would differ at the different volumes, so you'd have some difficulty keeping the two amps at the same volume comparatively at all times, even with careful gains adjustment.
Maybe there needs to be some clarification:
If you use one amp running your left splits, and a different brand/model to the other amp running the right splits, there will be a noticeable difference in volume/sound.
However, using one amp for fronts, one amp for rears, won't be noticeable.
"Vertical" amplifier differences are unnoticable (viewing the car from the top down), but "Horizontal" amplifier differences are likely to be noticeable.
EDIT: Running one sub with two amps won't be able to be heard (as above), but the sub could sound muddy. It's different if you're running two separate subs (same type) off different amps.