2 exact same amplifiers to 1 dvc sub?

This is a misconception I had for a very long time too.  The truth is as long as you do not exceed the thermal power rating of the voice coil, it can remain stationary without damage.  Two signals 180 degrees out of phase at exactly the same levels applied to a DVC speaker will theoretically result on zero cone movement, and the end result will simply be heat.  But no damage will occur unless you exceed the speaker's power ratings, and then damage will occur anyway.  So the reason to match the signals going to separate amps used to power a DVC speaker is to minimize self-cancellations that will limit output levels.

i may have overread it but im not sure if anyone gave the writer of the post any ideas on how to properly set the gains so that you know for certain that both amps are putting out the same amount. as we should know, not all "3/4 of the way up" are equal.

one thing I do in these rare occassions that I actually have to put an amp on each coil is use my DMM and measure the voltage output of one amp at the bridging/mono channels (without anything connected) with it set at whatever level I'm wanting it at. Then I match the voltage on the second amp to the first. Once matched, I connect the coils to the amps. This way, you are certain that the output is equal for the best results.