Quick reply, as I'm mobile ATM. A few important points:
1. There are also piezos involved (or will be soon), which ups the stakes considerably. You can DI the piezo to the PA, but it becomes difficult to control and balance when there is a guitar amp involved too (ask me!). Putting the piezos through the guitar amp limits the tone substantially.
2. Back problems IMO preclude a two amp (1 electric and 1 acoustic) solution. Also if you're playing in church, it's a very controlled environment (especially AFA volume is concerned) and not conducive to having a couple of live amps on stage with you.
So, all told. I'd recommend another, better multiFX unit. Vox usually get my vote for electric guitar, but the new POD HDs do look interesting and come highly recommended by some whose opinions I trust - so worth a try at least. If you want to run piezos and magnetics through the same unit and see it as an either/or setup then you can use one multiFX for both, just writing some patches for piezos (without amp or speaker modelling). However, ideally you split the piezos off to their own processor, then you can blend acoustic and electric patches together. That's where your Digitech will come in handy - while I'm not a huge fan of their amp and speaker modelling or distortions, the delays, reverbs and modulations are good - which is exactly what you need for piezos (same story with the Boss stuff IMO).
So in short, upgrade your electric guitar MultiFX and use your Digitech for the piezos... With a nice full-range system (the PA, studio monitors, a powered stage monitor), you get the best of all worlds.
Dinosaur Snr wrote
or event maybe the TC Electronics Nova System.
Much as I love TCE, the Nova does not have amp modelling, but is made to use up front of a real amp and speaker.