It is possible to configure the time line, bigsky and hx stomp so that they work at the same time in a footswitch of the mc6
Yes, I use all 3 and they all work fine with the MC6. Just assign each to a separate midi channel and be sure midi thru is enabled on each so that commands can pass down the chain from one to the next.
You can assign one or more devices to a single footswitch if you like. PC commands will work for changing presets and CC commands for changing any other features.