That's a tough proposition.
I don't think there's a huge user- or knowledge-base out there when it comes to sync'ing up two 388's, though the 388 is capable of master/slave sync.
All I know is you'll have to start with the compatible Elco-type connector, (can't remember how many pins, but I think 56). Then there's DIY cabling to the proper pinouts on the connector, the details of which are in the 388 manual.
The other half of the equation is finding the most compatible synchronizer. I don't have a firm notion of this, other than I think the Tascam ES-50/ES-51 Synchronizer/Controller should be plug-compatible. The 388 runs on a PARALLEL interface for sync. That's a key point.
I think another Tascam sychronizer, the MTS-500 with IF-500 parallel adapter might work. I also think the MTS-1000 MidiIzer with IF-1000 parallel interface will work, too.
There may be a way to adapt a Fostex 4030/4035 Synchronizer/Controller to a Tascam 388, but that's [IMO] unproven and would require significant reverse engineering. I think the Fostex sync required a special 'pigtail' Tascam IF adapter cable, of it's own, which are extremely hard to find! Tascams and Fostexes didn't alway play well together on the schoolyard, and that was a concious marketing decision by both compainies.
Not to mention, the 388 is a unique breed of it's own, which is fine in some regards, but complicates other issues sometimes.
That's pretty sketchy info, but I hope it helps a little.
