The IPAC is 8-10 years old, and has two PS2 connectors on the board. One for connection to the keyboard input on the PC and the other as a keyboard pass thru.
Stuff I'm reading says the PS2 uses 5v and USB is 3.3V.
I don't mind replacing it. While I'm a cheapskate, I really don't mind buying a new one. The IPACs are really well supported, both by the vendor as well as the community.
For that matter, its not the end of the world if I go with the ControlBoard and if I hate it, just buy the IPAC later.