At one point I had an SM2 and an fx8 and had that hooked into my amp. I'm sure it is similar but the labels are likely called something diffferent
Forget the fx8 at first and take it one thing at a time. You may also want to try a mono setup and/or just 1 syn2 to get things going.
Get #1 syn hooked into the power amp- that should be easy. This is your host amp.
Now get #2 syn hooked into the loop of Syn#1. Make sure that you have it hooked in right and can access all 4 of the channels. Basically, host amp will switch between ch1, 2 and loop. Loop will then access #2 syn ch1 or ch2.
Once all that is covered:
the fx8 amp out should go into the #1 syn guitar input (treat it like the input of an amp)
Now here's the part that always made my head confused
you need to put the fx8 send & return between the #1syn output and the input of the power amp.
guitar goes into fx8 input
This should give you ODs and other stuff before the amps and delays/reverbs after the preamp
I hope that helps!