I called them last week because I was in the same boat, they said yes it will be stackable... depends on how much power you want.. this is a very noticeable change, and the best part is it doesn't void any warranty, you may be just run this set up and call it good. But then again it all depends on what future tunes will do to it
maybe we talked to 2 different people and only 1 knows what they are talking about..haha here is what i was told.
"The pedalmax will not be a problem. The boostmax must only be used with a custom tune that takes the boostmax into account or you will end up with too much boost. Now once custom tuning is available through sct we will be able to custom tune the truck around a boostmax so that we control boost with it and everything else( trans shifting and rev and speed limiters) with the tune."