i looked into this a while back. LR Baggs, who made the Double Edge saddles for Ibanez, does not make any piezo to midi components. RNC makes piezos and midi preamps for installation in a guitar [the Brian Moore guitars use their hardware], so i contacted them. they were not helpful at all, giving an arrogant sales pitch about how their piezos are highly superior [but of course they don't make a piezo saddle that will fit a locking trem]. when i pushed, they said the Baggs hardware is too weak and noisy to use with their midi preamps.
theoretically, there should be a way to get midi output from the Double Edge piezos, whether the Baggs is lower output or not. the fact that an Ibanez Double Edge model comes stock with a midi output [does that GK in the model # mean they used the Roland GK2 preamp system?] shows that it is possible. i looked at schematics of the GK2a, but i didn't have the stones to spend $300 on one and then cut it up to try and hack it into my Double Edge.
if you dig around and find anything more hopeful, please post it here.