Steve's right,
A cluster would be 1xA5200 connected to 2xE4500 (example)...
If you want to connect 2xA5200 to a single E4500 then, as
Steve says, it's a case of either connecting them to seperate controllers as individual arrays, or daisy-chaining them together, numbering the A5200s 0 and 1 (via the front panel) and connecting one end of the daisy onto your E4500.
Let me know if I can offer any advice.
Darren