Not used the ELC Node6 myself - but it sounds like that might work.
The Luminex box has a function to be able to switch between 2 controllers via a single DMX chanel trigger - which is how I've done it in the past.
My only thought is that an LTP merge may not be ideal if the 'other' controller changes - a switch function might be more reliable...
However, If you only have static colours programmed on the MA - it might be easier just to re-program those cues using catalyst/pixelmad as the controller (very easy) and have the stage bars permanently connected to catalyst - thus avoiding any merging or switching scenarios.
Simon