I agree with msttomservo, FX loop is IMHO best way to go. You can also have regular pickups - electric guitar going to DT25 and piezos - acoustic guitar going to FX loop at the same time using dual signal path  - just use fx loop in path with acoustic guitar. With propper settings you can blend those two sounds or do nice and fast changes from eletric to acoustic sound.

I just ommit the amp completely on acoustic patches. Then there will be no sound routed to the DT25 even though it is connected. On electric patches I set the mixer after the amp to zero volume. That will turn off sound to the PA and only route the sound to the DT25.

I've also created a second bank of patches with the only difference that the volume is not turned down in the mixer after the amp. I use that for playing without the amp if I don't want to drag it along. Then I get all the sound through the PA using just the JTV and the HD500.

Good luck with the programming.

Best regards

Soren