Whatever, there are still some misstatements above but this has resulted in a long tangent from what the original poster asked.
For the OP, since you are considering ways to move to a stealthier setup:
I personally have run AT853s via:
straight 2 wire - They do clip, although not as easily as some believe. In 2 years (note: using a 9V battery box. Using lower voltage PIP from a recorder's mic input may cause more problems) I had one recording badly clipped, but I try to avoid concerts that will inevitably damage my ears.
3 wire battery box - this did drop sensitivity considerably, I never measured it, but 10-12 dB sounds about right. This means I had to add more gain via my recorder. In theory this meant more noise, in reality the noise was usually buried in the ambient noise at moderately loud concerts. Ironically, the only shows I could hear the noise on were the acoustic ones with very quiet, attentive audiences - the ones which never would have clipped before.
4.7k mod - sensitivity was very close to the 3 wire version. Despite what some people claim many people hear, I heard no difference.
So again my advice is get some better open mics if you want better sound. If you want a stealthier setup, don't bother with 943s, figure out a way to run the 853s with a smaller recorder.
Personally I very rarely stealth and I'm not "afraid" of an extra box, sometimes I just want to keep my setup as inobtrusive and uncluttered as possible. Again, if you want to maximize sound quality, don't worry about how to power AT853s, get better mics.
Edit: If you get a custom made 3-wire battery box or preamp with mini-XLR inputs and a miniplug output, you can run your AT853s (sans the adapter/XLR part) into a smaller recorder like an R09 when you need stealthy, and keep the phantom adapters for when you want to run the FR2LE. A PS-2 modified to have a miniplug output, or with an adapter cable, will work too if you also use the adapters. That's the way I'd go if you want to keep the AT853s as your main mics, both open and stealth. And I didn't mean in any of my comments to imply I thought AT853s were bad mics - I love mine. But you can do better.