I delivered an LCRS mix to a post house today who are trying to transfer it onto digibeta via Avid's Symphony. This digibeta only really needs to be decoded by a Dolby CP50 SR system (with the digital add-ons) and they are putting a seperate stereo mix onto the same tape

As requested I gave them 4 seperate AIFFs and have now been told that the op can't guarantee that Symphony will route these to the right channels and that I should encode them differently, tho they aren't sure in what way. Research has suggested I'll need to encode a Dolby Lt/Rt matrix which will be put on tracks 1 and 2 of the digibeta and decoded in LCRS by the CP50, leaving tracks 3 and 4 for a stereo mix. Is this correct?