L&R subs but only only a mono sub output; options?

This may be difficult to explain correctly but I may be in a situation where I have two subs and two monitors functioning as L&R main speakers. The subs will have plate amps with RCA inputs but I can only output a split mono sub signal from my receiver. I don't want to go this route since I will loose the stero effect for anything below the crossover point which may be higher than usual due to the overall design.

The only other full range signal that I have available would be the preout for Zone 2. In theory i could run the zone 2 preout to the sub to deliver the signal and use the crossover on the plate amp. The trouble here is that zone 2 only plays analog inputs which means connecting up analog cables from my BD player and cable box...not a problem in itself but will there be timing issues in the output signal due to the different processing and delivery of the inputs?

Hope this makes sense and looking forward to feedback and suggestions.

Do the plate amps also have speaker (high level) connections? If so, you should be able to run a set of speaker cables to your subs from the same speaker connections on your amp that your monitors are hooked to. The high level sub inputs are generally high impedance, so the amp will easily drive this load. Adjust the crossover level on the subs (lower usually blends better). The monitors will run full range. I have my sub hooked up this way with my Magnepans, and it sounds better than using the low level (RCA) input.
Yes they do, I assumed it would have been more flexible using the RCA since I could run the onboard eq from the receiver and set the best crossover electronically but the more I think about it the more this makes sense; I would just have to set the crossover on the plate amp right? These can now be treated like 3-way full range with powered bass and if I need more bass I can add a true sub to handle the ultra low stuff.
You could run the full-range zone 1 pre out into an active stereo x-over like the NHT X-2 (discontinued, but available used from time to time) or similar.

I tried to understand what should be relatively straight forward connections in HT only to get frustrated and lost, repeatedly I might add. I must have assembled 100s of stereo set ups, even with tape loops back in the day, with no problem.
I really don't know why it is that the manufacturers of these pre/pro things wants to keep confusing to the general public but they manage to baffle all but the best of us.
You need a preamp with 2 outputs for subs alone, which you can hook up as left and right stereo channels to the subs amplifiers. I guess you might have better results on a very dedicated HT forum elsewhere. Perhaps even begging the manufacturers to tell you who has that feature if they don't.
I am as I explained a 2 channel fuddy duddy who doesn't usually like even the addition of 1 sub for music applications. In HT it can be a lot of fun.
I think most of us who use two subs do so for smoother LF, and doubt the stereo effect of such LF. Most of us cross to the sub just above the effective LF extension of the mains or use the THX standard 80 Hz.