I have a Fender Acoustasonic Telecaster that has a piezo pickup in the bridge position and a magnetic single coil in the neck. It's set up so that you can split the signal using a stereo to mono Y splitter jack cable, with the signals from each pickup on its own individual mono jack.
A thoughtful poster proposed the theory of being able to use the return input on the kemper for the piezo signal, then set up a mono loop in one of the slots after the stack. That way you could get an electric, driven tone using the neck pickup going into the main kemper input as usual, but then the more acoustic piezo tone would feed into the kemper bypassing the stack, giving the option of the clean tone and the ability to mix the two at the same time, depending on the position of the pickup selector on the guitar.
This would be fantastic. However, having just experimented with it, it seems that the Stack section influences the X and Mod slots, even though in theory any signal arriving via a loop to one of those slots should be independent. Turning the Stack section on and off while playing through the loop set to 100% mix changes the HF, giving the effect of turning cab sim on when the Stack is engaged, and off when it is disengaged.
This is all very perplexing and slightly perturbing, as it would then suggest that any pedals or effects that were in a regular loop after the Stack would be sent via part of the stack anyway, in effect doubling up on the Stacks influence (your signal passing once through it on the way out of the kemper through the send, then once again after coming in through the return). What gives? I'm running the latest firmware, by the way.