If you read some of my other posts, you come to the realization that twin M5s per channel with an ADA-1500 have 11.5 dBC more output than single M5s per channel with an ADA-1000. 3dB of this 11.5dB comes from stacking the M5s. The remaining 8.5dB comes from replacing the 1000 with a 1500.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated