I dont want to get too much off topic but you can measure the amp's efficiency.MMATS is good, but far from the best, and no amp is 98% efficient except for the Rockford 15000 which is a completely different animal. And I dont remember seeing anyone with MMATS amps at the last 3 World Finals I have been to.
Jest play a test tone at full volume. Test your DC voltage drop and current draw at the DC power input. Note those measurements (you have noted 262A @ 13.8V) Then do the same measurements on the AC output side of the amp. Use your clamp on ammeter on the speaker wire, then measure AC voltage output. This will tell you your real wattage output.
Also, those subs are good, again, far from the best. But they look great and beefy and perform outstanding.