I did take some quick measurements comparing these with my old subwoofer. I'm beginning to think there's some pretty heavy room interaction causing that peak at 50 Hz since it affected both setups (one of the MFW-15's is in the same position as the H100 was). I didn't add any offset to these measurements, and I tried to match the levels as closely as possible, so you can see that I don't lose any output at all from the switch to sealed from ported (not too surprising since I added a second sub). I did gain a lot of extension, though, which is what I was after.
I hope everyone enjoyed watching this process as much as I enjoyed carrying it out. I'll keep you up to date on any new projects I come up with, but for now I'm taking a break.