I don't have experience with the Sundown but I hear great things about them.. Mmats on the other hand I have a bit of experience with. For example, I had a pair of Mmats D3000.1s and a pair of the 04 version of the dual 2 ohm 15" Solobaric L7s. (silver cone with blue logo) When I first got them, I wanted to hear what they would do, I put the subs in an 8cf box tuned to 32HZ, subsonic 24HZ.. I hadnt run the big 3 yet, the box was crap, made from a combination of 2 boxes put together...
Stock alternator, only a 4 Guage running to an optima red in the back of my Jeep with a digital cap, epic 160 for curiosity.. The two mmats amps running off the stock alt and wiring with only a 4 Guage and Optima put up 143 playing bass mekanik and I never saw the voltage drop below 11, stayed in the 12s on music mostly, started to get critical when I got down to the low 30s with the test tones, then I had to lower the volume... I remember seeing 138 at 32HZ or something like that.. Again, not accurate, insufficient wiring on stock alt with Mickey Mouse build. Plus this was 2 years ago and my memory is shot..
I was running Mmats comps up front (already installed in work truck) with a mmats 4 channel and PPI frx456 crossover, alpine deck.. The output was absurd considering the Mickey mouse build and lack of current, not to mention the SQ which crushed my buddies all JL system which he paid over $5K for.. I know the epic 160 isn't accurate, but I used it for ballpark and out of curiosity and that was the reading I got..
The Mmats amps are incredible, I don't recommend doing so but they will wang with a stock alt, and they will do it clean and controlled, highly regarded in both the SQ and SPL crowd.. Build quality is great, they use expensive components, Toshiba output devices, oversized same as Linear power DPS.. Another thing, these barely get warm even when pushing hard enough to make my neighbors come out and complain at noon on a Saturday (they live down the block) I drove around that day then I took the system out that night..
The correct install happened a few weeks after that. I ran the big 3, built a 4 CF sealed box, ran proper 0 and 2 Gauge wiring, installed 3 way front stage with 2 mmats 4 channels, 1 bridged to ID8s, the other as a 4 channel to Boston Pro 5.25s, PPI FRX 456 crossover with alpine deck, pair of Mmats amps, 1 per Solobaric.. The best sounding system in my neck of the woods for sure.. I routinely compared it to people that paid 4K or more for their installs and usually got a lot of compliments from both bassheads and SQ people.. Never did compete.. Mmats make amazing amps, good subs and decent comps.. In that order..