When using the DR2d line-input for SBD patches I've pluged an extra pair of Countryman B3s into the low-voltage powered mic input mostly because they were sitting there in the bag, why not.. gaff taped them wide spaced to the soundboard enclosure, back wall, etc. It powered those acceptably each time.
But my standard rig with the DR2d is two Curch CA-Ugly preamps, one into each input for the smallest 4channel low voltage preamped recording rig I know of.. as long as set gain is cool. I just set the gain beforehand and don't plan to adjust it. Know the rig, know the gig, aim to peak -12 to -18dB and how often do you really need to adjust gain after you've been doing this for a while? Nice little package for that. A single, tiny 4 channel amp would be even more trick though.
BTW, I only use it to start & stop recording, but you can adjust mic-input gain with the IR remote any time you like, even when the hold button is locked.