Me too!
I bought 4 388's, with the same intentions!
So far, I've not achieved this lofty goal.
I know you'd need an appropriate SMPTE sychronizer and cables.
I've ventured to start on this project, by scoring a Fostex 4030/4035 Synchronizer/Controller, but I found out too soon that there's a specialized Fostex-to-Tascam adapter needed, the Fostex 8785 Interface, which is a seldom seen and hard to get item.
I think, in my own case, if I'd successfully score the Fostex 8785's, I'd be good to go on the 388-megaplex-sync project, using the Fostex synchronizer.
Otherwise, I'd recommend researching vintage TASCAM synchronizers, and you'd probably simplify the task, greatly, by sourcing a Tascam-to-Tascam compatible solution. I'm not familiar enough with Tascam Synchronizers to quote model numbers, but I'll throw in, to the best of my recollection, the Tascam ATS-500 and the Tascam IF-500. Verify those model numbers before purchase.
When I have time, I'll research and post more. I'd love to do this, 388-sync, as much or more than anyone on this board.
Thanx