Hi aL,
in Logic, I could not have multiple mixes of the same tune within the project. To do so I had to save different mixes (even if they're ever so slightly different) as separate projects.
Like anything with Logic, you can, it's just involved. If you wanted to duplicate your tracks, you could stick the duplicates in folders. Each duplicated track gets its own channel strip, and you could then adjust them slightly for the alternate mixes, etc. To select an individual mix, you'd solo that folder.
Personally, I would much rather have a different song in the same project folder anyway--it would help me keep it separate. I'm actually working on an EP right now in which different artists are contributing completely different mixes/arrangements, and I would hate to have it all in one project!
As for the midi implementation in Logic, I found it to be difficult to use (to say the least).
Ironically, that's why I stopped using DP around 3.5. Coming from Cubase, I couldn't get my head around the "American" style of sequencing of DP, I was so comfortable with the region-based MIDI editing of the German sequencers like Cubase and Logic. DP has "phrases" but it never let me cut and move around regions of MIDI notes the way I wanted to.
The environment looks and acts somewhat archaic
Depending on your needs, you'll never even need to look at it.
But, I have at any one time 6 or 7 keyboards which I trigger from multiple keyboards (and not in the same combination every time). To change the triggering and destination keyboards seemed like a total pain. But, I can't claim I was a power Logic user.
Again, I'm not 100% sure what you want to do, but if your needs are basic enough, you can try creating a software instrument track, and assigning an External Instrument. You simply set the MIDI in and MIDI out and Audio In and Audio Out on the External Instrument plug-in to your keyboard you are triggering, then play any other keyboard you've got to trigger it.
For example, I very often will:
1) Create a software instrument track
2) Add the External Instrument
3) Have it send MIDI to my DSI Mopho (monosynth)
4) Have it receive audio from my DSI Mopho
5) Play my DSI Prophet 08 keyboard to trigger the Mopho
I never need to play in the Environment. It doesn't get simpler than that.
I think Logic's handling of external MIDI instruments, thanks to the External Instrument plug-in, is the best in the biz. You'll need the environment if you want to do advanced key switching or whatever, but not for just using multiple keyboards to trigger other hardware modules.
Orren