Q: Being that the MFLA is rated to sustain 136dB, would invert-arraying a pair of DV12's get me to 136dB from 126dB as a non arrayed DV12? Would arraying 2 MFLA cabinets together add 10dB and would adding 2 more MFLAs effectively double the volume once again?

Arraying a pair of speakers ordinarily results in an increase of 6dB if their output is coherent, which an array of DV12s, an array of MFLAs and an array of most subs would be. An array of 2 "point-source" speakers (such as AT212s, DiaMons, AT312s and most other non-line-array speakers in the world) would result in a 6dB increase at low frequencies, where the output would be coherent, and an increase of only 3dB where their output would tend to be incoherent, in other words, where their outputs would begin interfering with each other. (aka comb-filtering.)

The woofers in the MFLA are more efficient than the woofers in the DV12, so they can sustain a higher SPL. Two DV12s would get you to 132dB. (The low-frequency drivers are usually the limiting factor in the output SPL, which is why some manufacturers claim such high SPL capabilities for their line-arrays and tops: They measure the maximum SPL that the tweeter can provide, or at 1kHz, where both woofers and tweeters are contributing, without considering that if the woofer(s) can't keep up at the bottom end, the sound character changes and the result doesn't sound good at all.)