I believe it's 30 watts per channel into 5 channels. The woofer gets its own channel, and the dash tweets are in parallel with the fronts. Since it's unspecified, I'd bet that's 30 watts peak. I'll leave it to you to do the conversion to RMS.
The stock speakers are rated for 30W max (see Bernie's install pics that show them clearly marked). These are the same Alpine speakers that are stock in the MDX. Many of the MDX folk replace them with the Infinity 652i, which fits in pretty easily.
The woofer is somewhat of a pain to get to, since you have to remove the rear door sill trim, the tailgate sill trim, the D-pillar trim, and the 3rd row seat before removing the side trim panel.
For a quick hit, upgrade the speakers to improve sound quality dramatically. This won't address the power limitations, though.
Yes, I guess if I were going to listen to the MB Quart at low levels the 30 watts (if that's RMS) would work. However, all the research I've done, indicated to drive the MB quarts QSD mod to mid or higher volume levels require 60+watts RMS.