Consistent audio breakup/stoppage using a 2nd 192 I/O

[firmflange]

I read the manual and did a search on this and couldn't find the solution, I am still a beginner at HD and could use some help:



Running PT 12.5 HD Native Yosemite 32gb ram:

Upon playback, there is a breakup, then a stoppage....then I get the -9172 and -9129 errors, (clocking issue) asking me to verify sync cables or change buffer sizes, which I've already done. Do I need a loop sync cable? I thought you didn't need one if you're just syncing 2 192's?

I'm running HD Native for several months now without a hitch until I connected a second 192 (both 192's are analog, not digital). I connected it up per manual directions (Card > 1st I/O Primary, 1st I/O expansion to 2nd I/O primary)
Both 192's are recognized in the Hardware window.

Tried all buffer settings. Clock source is Internal on both units.

Problem exists in every session now, where as it worked fine when I was using just the one 192, so I think it's relative to a mistake I'm making hooking up the 2nd 192. Any help appreciated.