How about using an interconnect cable between the racks. You will not need a second CPU. I have two 13 slot racks tied together this way. Up to 3 racks can be tied together.
I have done something simular in a project I did this
send a 1 to N111 and bit 0 energizes
send a 2 to N111 and bit 1 energizes and turns off the other bits
send a 4 to N111 and bit 2 energizes and turns off the other bits
if you send a 0 to N111 it turns off all the bits
if you want two bits on...