
I use it to access a UAD-1 on a G5 when I need those effects, to use an old version of DSP-Quattro to host old 32 bit VIs and plugins that won't work in DP, and to use the Harrison MixBus channel strips in DP. Generalizing this approach can be useful. You might have to play around with a delay plugin on the MIDI channels that go to Mainstage to get the timing right. From then on, it all pretty transparent, and you can do most stuff with the other App sitting in the background. It's tedious setting this up the first time, but once it's done, create a DP template, and save a project or template for the other App as well. It should be possible to find it with a search for Mainstage. Mainstage doesn't access the Environments, but someone here posted details on how to deal with MIDI channel. In Logic you can put some MIDI processors in the Environment to direct different MIDI channels to different instruments.

Less obvious is how to get MainStage to respond to multiple MIDI channels properly. MainStage no longer hangs: When the Add Patch (+) button in the Patch List is clicked. Stability and reliability Includes stability and performance improvements. I posted links to DP and Logic templates here a few years ago. MainStage 3.5.2 New features and enhancements MainStage now displays an alert if the computer power supply is disconnected in full screen mode. I do this to access EXS24 in Logic in DP. You can use the IAC driver for MIDI, but the DP interapp MIDI feature works too. You need something like Soundflower, although I suspect JackOS would work too.

Or any external application that uses CoreAudio and CoreMIDI. You can use the same setup to use MainStage in DP. There's an article on the MOTU site, maybe in tech support, that tells you how to use GarageBand in DP.
