IMHO, considering the mics you are running off of, and that you have the Church pre, I would consider maybe either (a) upgrading the mics first or (b) upgrading the deck to an M10 or something like that. Fine, it's not all digital, but I think CA9100>M10 would sound pretty great. The D50 seems kind of pointless if you do a lot of lowpro work and the only reason you want it is the digital in. Not knocking the D50, just don't think that makes much sense for you.
Personally, I'd see if you like any of the mics that are possible upgrades to the 853s, like the Audix 1280c with church cable (arguably an upgrade, depending how you like the sound of it), an active setup involving AKG ck91 or other similar types of caps, or maybe the Countryman B3 (no personal experience, I just know Richard likes them a lot).
Or, I'd put an M10 behind the CA100 or UA5... Mainly just so you have a deck that's 24bit, has a better ADC, and isn't HDD based. I'd also consider cheaper options like the new Tascam DR-08 also.
Littlebox is nothing to shake a stick at, either (love mine).. I just think you are probably, for lowpro work, better off relying mainly on the 9100.