Matt,
I would use the M6start and M6End macros to accomplish what you want to do. You will need some logic in the macro to look at the selected tool and decide what spindle goes with it. Then turn on the appropriate output to your relays. Prepare yourself for confusion. I would check out the mach customization docs. Also have a look at the Wiki and the mach2 manual. The info you need is spread out all over the place.
You might also find my turret macro helpful to get an idea how things work:
http://www.machsupport.com/forum/index.php/topic,12990.0.htmlBrett has been reorganizing all the inputs and cleaning up the OEM button and DRO naming conventions for Mach4. Lets just say that it is rather organic in its present state.
The offsets to the spindle in use will be in the tool table.
So when you call for T0110
You are asking for T01 (spindle #1) and offset 10 (can be 10,11,12 etc) so you would have offsets for various tools in spindle #1
T2 can be spindle 2 etc.
Monty