Not knowing your CPU type nor the GPU's, I took a stab at it.
If the CPU will run hotter than the two GPU's combined, then a routing of the
Pump -> CPU -> Single Rad -> GPU -> GPU -> Dual Rad -> CPU would be an option. I agree with Bill by allowing the PA160 pull the air upward an out of the computer case. The old saying in thermal dynamics is, hot air rises to the top. So, naturally, let it out of the top.
As for the single rad location, the fan between it and the lower front case should pull air "in".
(edited for grammer)