I am not 100% sure what you are looking for, but let me throw something out to start the conversation.
As to the physical layout of the loop the following is an option:
Reservoir -
Aqualis base for pump adapters 880 ml
to
Pump -
D5 Pump with USB & Aquabus with
pump adapter for D5 pumps
to
Radiator 1 -
to
Water block 1 - GPU 1
to
Temperature sensor H2O 1 -
internal/external thread G1/4 for aquaero
to
Radiator 2 -
to
Water Block 2 - GPU 2
to
Temperature sensor H2O 2 - internal/external thread G1/4 for aquaero
back to
Reservoir
You may also want an ambient air temperature sensor and radiator exhaust side air temperature sensors.
The D5 pump would plug into the Aquabus high header on the Aquaero 6
The temperature sensors would plug into the temperature headers on the Aquaero 6
All fans would be pluged into the fan headers of the Aquaero 6.
You specified a Bitspower reservoir but not a pump top. for efficiency and easy integration, you may want to change the reservoir to an Aqaulis reservoir ready for a D5 pump top (linked above).
Variations of the linked items are available as to capacity or features (i.e. LED, fill level indicator).