Welcome to the forum.
Unfortunately, PrE cannot Encode to DD 5.1 SS for Export/Share.
Even in PrPro, one needs the optional Minnetonka Audio/SurCode DD 5.1 SS plug-in (about US$ 250) to Encode the multi-channel Audio to DD AC3.
PrE can Import DD 5.1 SS, but will mix-down to stereo (2-channel).
Thank you. Was wondering if that was the case but thought I might have missed something.
No, unfortunately you did not miss something.
The same, or very similar, question comes up in the PrPro forum, quite often. There, it's usually along the lines of "why do I have to buy the SurCode plug-in? Why is it not included in the price of the program?" There, the answer is that if it WAS included, the price would go up by about US $ 250 for every copy of PrPro, whether the user ever needed to do DD 5.1 SS, or not.
Personally, I was so impressed by the SurCode plug-in for PrPro, that I bought two licenses (no discount for multi-user licenses), and nearly every Project contains DD 5.1 SS, that gets authored in Encore. I also got the SurCode DTS Encoder (not a plug-in, but a stand-alone), and many Projects also have DTS as a supplemental Audio Stream.
Not sure if PrE will ever have DD 5.1 SS output, due to the cost of the DD licensing.
Now, some NLE programs DO offer 5.1 SS, but not sure how many are fully DD (Dolby Digital) compliant.