I can see from your previous posts that you've had some trouble getting your head around RMX. So the FIRST thing I want to say, one "anonymous" user to another, is that "I feel your pain" -- you know?
There are a whole lot of us who keep discovering new features in this monster, and I know I'm not the only one who just finds myself sitting here, mouth agape, in AWE of what they've packed into this thing. It's an amazing instrument/sample set, with so much flexibility and ease of use that my mind is boggled by it's superior implementation. And I ain't used to being no "fanboy" -- but dang it, RMX just blows me away. It just keeps getting BETTER and BETTER.
SO, whatever... I'm just trying to say, "hang in there" and I hope we can help you sort out your questions.
NOW -- maybe why you didn't get an answer earlier is that it's not entirely clear what you are trying to do, or what is not acting the way you expect it to act.
When you say "MIDI track 1-a, 2-b" I'm not sure what that means? Do you mean you send MIDI information on MIDI track 1 to part 1 of RMX? Or are you talking about the actual AUDIO outputs on the RMX mixer? I read your first "MIDI Routing problem" post but it doesn't help me understand -- sorry!
So please clarify what's up and we'll hopefully get to the bottom of this...
p.s.--I'm on PC, but also use Cubase, so we should be able to help each other...