Missed quite a few messages it seems!
I ended up picking the BDE over the DRZ route; through my research it seems like DRZ is much more appropriate for tech (deep walls and wrecks). My goal is primarily to see sharks so BDE should scratch the itch (never even saw an Oceanic White Tip last time I was there).
Last time I flew through CAI/HRG, I noticed that United/Star Alliance partners had the best (sometimes only) routes, so limiting your searches through those airlines should pull up the best options.
I actually found a convenient LAX-ZRH-RMF route on Swiss/Edelweiss, which works out perfectly. IIRC I think there is also a carrier from Germany (Lufthansa partner) and another in Scandinavia that fly into RMF from Europe. The other option was to fly into Cairo, then fly -> RMF on EgyptAir, but it would have put me in RMF like 3 days early. Not gonna lie, finding the flight schedules was a real PITA because these are seasonal routes that you have to wait for the airlines to update.
One helpful hint is that the dive boat schedules are built around the flight schedules, so if a dive boat is leaving on a particular day, there is very likely a flight coming in the day before. The Swiss flight schedule I'm on drops me in RMF the day before the boat departs, and it leaves the day after the boat returns.