Hi :)
OT:
Dunno why your Layla shows up as two independent sound-cards, however,
AFAIK when using a sound card with an ADAT device, just the optical
cable is needed, there's no need to sync by an additional word clock BNC
cable, as long as all cards are connected by ADAT.
IIUC there never ever will be perfect sync between cards using different
AD/DA converters.
My setup is based on a RME HDSPe AIO + a Behringer ADA 8000. IMO the
Behringer isn't a good audio device, OTOH at least my Behringer ADA 8000
is good for frying eggs. Some time ago I repaired a power supply for
another Behringer device, because it gets broken by undersized
semiconductors, that costs around 2 Cents.
Anyway, if I (would) use my ADA 8000, it (would) work(s) with jack, so
your trouble might be related to the issue, that your sound card does
appear as two cards.
Regards,
Ralf