Well you can run the relays instead of the solenoid. One relay per compressor, or a HD solenoid for both compressors.
Just make sure that 'noid does infact ground thru one of the terminals.
If you want to use relays...here is the schematic for that...using the ground interrupt....
You battery wire for two compressors should be at least 8 guage.
The jumper only needs to be 14-16 guage as it is only 'clicking' the relay...the same goes for the ground circuit leading from the cab to the air-system.