idea for a custom 7 string
You can. I've been in contact with RMC, and they will pretty much do what you need/want to set you up. The saddles (according to RMC president) will work extremely well as piezo/acoustic saddles, (just need an acoustic preamp. EMG, Fishman, L.R. Baggs, Graphtech, etc. make them. Could be internal or external, your choice) and of course, they also have synth capabilities. (I plan on using them for both capabilities in a project 7 as well.) Expensive, however. The Graphtech saddles may be the way to go. If you have a Carvin 7 with a fixed bridge, they'll work. I have no idea what the bridge structure is like on the AX.