I see, so you are thinking along the lines of setting up a sub spindle with a live lower turret on one controller, then the main spindle and upper turret on another controller.
There will be problems in case you want to start syncing though, but it would be cool as two separate lathe's where you do side one on the left and then side two on the right.
Mach is cheap, if you are prepared to spend on the hardware the extra cost for a second controller isn't an issue, but you won't get it to sync like a $30K controller.
From the swiss demo's I've been on what happens is you load two programs and they execute separately but both starting when the start button is pushed, at some stage one is given the command to wait for the other, they then sync and run a portion synced then after another command is given and they execute separately again until finished then both start again from the beginning when looped. It is the sync section that is important, which won't be possible. It is better for the controller to support 12 axis that can be separated in 6 x 6 than it is to run 6 x 6 and try and turn it into a 12.