The trick for aligning multicam recordings is to use the graphical representation of the audio track as a visual clue to "line up" the two (or more) simultaneous recordings.  (I think you have a setting where MEP lines up the footage according to what it "sees" in the audio track.  I don't know how "accurate" this is; personally I find it easier to do it myself, especially in the situation you have.)

So, in your scenario, I would place the tripod camera file(s) into the first multicam tracks, taking care to ensure the audio track is clearly visible by having it on a separate track (since MEP MX defaults to placing audio and video on one track.)

Then you will need to place the four files from your hand-held camera, in time order, perhaps one at a time (having checked via Preview which part of the concert is contained by each file) on the second multicam tracks.  You will then need to insert each file at something like the position it needs to be on the timeline; then you can use the audio tracks from the two cameras to physically align the handheld and tripod cameras.  (Once the alignment is "nearly there", choose a "very prominent" (= loud, if available) short section, zoom in so that each audio "peak" is very clearly visible and then slide the hand-held tracks so that those "peaks" match absolutely.)

This will be somewhat tedious, depending how long each of the four files is, but once you have done this and got all the footage properly aligned, since there will be gaps on the handheld tracks I would "lock" them in position on the timeline to ensure the alignment is not lost.

HTH

Jeff