Cool. I did look at the OM for the 3600...
EZSet apparently does EQ the sub(or at least it says it does)...
And, of course, in typical "owners manual fashion"...it says there is "manual speaker set-up"...but it doesn't show any of the setting in the manual...just "where to find it"...
Remove the EQ70. Once you set-up the 3600 using the pre-out, you'll only be sending 80hz and under anyway. The receiver should have(I've not read its manual) have 2-3 EQ "levers" for the sub anyway at 80hz and under.
You only need to split the signal once. So you are running "dual mono" into the...
Are these dual voice coil woofers?
If not, why are you running two amps, both in dual mono?
Also, the 3600 has its own bass management. You don't need the outboard EQ. (you probably did need this for the older Onkyo...as you were using outputs on it not designed for what you were using them for)...
Either I'm confused, or you are over-complicating it...or...you really mean two subs on each side...
I assume you mean to run the sub pre-out to a splitter to create two. Red/White(once run from a pre-out like the 3600 has) is irrelevant.
Do your subs(which are???) have red/white on them? If...
So in the last 9 hours of audios existence...
This...
http://www.amazon.com/Pyramid-RY6-Male-Female-Adaptor/dp/B0007LCKJQ/ref=sr_1_1?s=electronics&ie=UTF8&qid=1347974004&sr=1-1&keywords=rca+splitter+1+male+to+2+female
No longer works for your application. Nice to know a cable created 50+ years...