This is a question that was already brought up but it seems like it still stands.
There is a very distinct difference between auditioning a 5.1 mix in Studio through a stereo Windows setup and forcing the Master Bus to Stereo.
According to that previous post, the answer could have been that 2 different downmix techniques were employed (ATSC and SRS). However the same post suggest that SRS was deprecated with v1.11.
In other words, in the first case I am hearing LtRt and in the second I am hearing LoRo.
Is my understanding correct?