Well, lighting control was one of the parts of Landmark systems that actually worked some of the time...The wire, which is available directly from Lutron and other vendors, is not a standard configuration.There are two low voltage cable types commonly used in a HomeWorks system,
Two pair (one pair #18 AWG, one pair #18-22 AWG twisted shielded) Class 2 wire. Lutron wire model # GRX-CBL-346S-500 may be used, and One pair #18-22 AWG twisted shielded Class 2. The 4 conductor product is run to keypad and accessory control locations, the 2 condutor to dimmer locations.
I purchase my cabling from Liberty Wire and Cable for these systems. The wiring topology for a HomeWorks system is also a bit diffrent. The control busses are arranged in a Token ring fashion, with a certain number of devices (4 or 8) per ring and ending in a terminator.
I have attached the link to a HomeWorks Design and Layout guide that explains the system requirements and wiring rather well. Unfortunately, this is an older edition covering the first HWI systems. Current versions of HomeWorks documentation are restricted to the dealer side of the website, so linking them isn't very helpful. There are changes, but this should give you a good idea.
Two processors is pretty easy, you need to link them w/ the 4 conductor cable, set different addresses, and program away.