I have done this scenario hundreds of times and I always run 2 22/4 in the same conduit with other low voltage wire without a problem. Only one 22/4 is needed , the second one could run a siren, the keypad and the zone expansion module both use the same 22/4 keybus wire. If you are going to be powering several devices that need power you can use a PC5200 power supply module with a transfomer and back up battery to power your devices locally. Another option for putting a siren in the second building is to use a PC5204, its the same power supply as the PC5200 but adds 4 relays that you can use to power sirens, strobes etc...