Short answer is it worked, with no obvious problems, just not sure yet how well. These are on-going experiments for me. Nothing conclusive yet. Haven't really had the opportunity to play around with the resulting files.
Longer technical answer-
I had a recording opportunity the evening following my query to John above, and another 2 weeks later. Since these were quick proof-of concept type tests I ran to the dollar store, bought a pair of one dollar headphones to scavenge the stereo miniplug cable, and soldered up a couple XLR connectors to power the two X-8S "single ended" (floating pin 3, grounding pin 1, +9V applied to signal pin 2) though an unbalanced 9V preamp (a Church Audio CA-UGLY v1). Sensitivity was reduced as expected, so I set gain on the preamp to the maximum available ~+20dB. That worked, with no obvious frequency response problems, self noise problems, or interference noise problems apparent on a few cursory quick listens to the X-8S channels. However I don't currently have a computer setup with audio editing software on it so I haven't had a chance to manipulate the files as necessary for actual listening and assessment as M/S pairs in combination with the boundary/baffled omni mids. I only listened to make sure it worked without obvious problems.
These files were recorded on a second small 4 channel recorder run concurrently with the primary recorder, and a delayed copy of the intended Mid mics from the first machine were routed to that second recorder. The headphone/monitor line out from recorder one was routed to line-in of recorder two, and the A>D>A>D delay inherent in that signal chain caused a delay between the Mid files and Side files recorded on the second machine. That was expected. I'll either delay the X-8S files to time align them with the Mid files recorded on the same machine, or use the copies of the Mid files recorded on both machines to help sync the X-8S files with the files from the first recorder. Wrap your head around that one for a minuite.
Yeah, a crazy convoluted setup requiring post work to listen to correctly, but these are just tests to see if perusing this idea further is worthwhile, and the only way I could record a third pair of mics with a relatively small pocket-able rig using a second DR2d, which didn't compromise my standard 4 channel setup.
^
Please keep in mind that this is not Jon's recommended powering arrangement for these mics. I plan to run these again in a couple weeks at an outdoor music festival with a proper balanced connection and P48 powering, similar to my first test recording with them, but as part of a different multi-microphone array. That will be recorded into a DR-680 so there will be no need to do the two recorder sync and time alignment thing.