Ok so I purchased a Cosair CX750M this morning. It works with the paper clip trick and seems to be running 2 cubes just fine. However, the power wasn't the issue causing the poor performance. It is nice to have 2 units on one power supply and not have to run it off a computer though.
My LAN was on the 172.0.16.* subnet and it appears that any stratum proxy hates this (even if the cubes are configured to point at the proper address and do connect - they will under perform).
After moving to the 192.168.1.* subnet, the units are hashing at a combined 59-64 GH/S (in low mode).
So you must be on a 192.168.*.* at the very least . . .
The IPs should not matter as long as you are using the correct private network addresses and everything is configured correctly.
The 172.0.16.x network is part of the AT&T U-verse network, which is a public network.
Did you mean to use 172.16.0.x which is for private network use?