+2dB is just the level in relation to the rest of the speakers, and no indication of its power output. You have the gain on the AV receiver for the sub channel, and gain on the back of the sub itself.
The Magnat is also ported, which means you’ll be hearing certain frequency ranges exaggerated, possibly even with a fairly high level of distortion - a sealed sub won’t produce these distortions, so can sometimes sound a bit lean compared to a ported sub, but all you’re hearing is cleaner bass with distortion or coloration.