Going back to the original post, one thing that wasn't touched upon at all and that I don't really get is why it is such a big deal to export "dry tracks". I suppose you would need to disable some plugins (most EQ and compression) and keep others active (signature delays etc) but other than that it's an operation of a few clicks and perhaps a cup of coffee if it's a particularly large project. Maybe I'm misunderstanding or maybe the OP is taking some unnecessary detour?
I totally understand a producer wanting to work in his preferred environment by the way. If I'd have to mix/remix someone's stuff I'd ask for stems and put them in Sonar too. It's just quicker for me. Even though I'd use the same combination of FabFilter/Waves/whatever plugins. And for others, especially if the DAW is relatively unknown in top level circles (like Sonar), it's understandable that they'd say "no" because they don't know if the platform is "pro enough" to get it to their level. Basically, they're insecure. But I'd be too if someone asked me to deliver release quality stuff and they started their project in Magix Music Maker.