Audio transcoding options for slow internet

Hi,

i've a plex remote setup streaming to a slow internet connection. Relative slow because i can stream Full HD from netflix.
I do stream mainly on samsung smart tv, most of the time 5 on 12 is the highest quality i can reach.

In this situation i can stream, assuming i can use all the bandwidth, more or less 2,1 GB for a 1.30 video content.

In my case video quality over audio has the priority, so:
1) is it possible to force transcoding of the audio from DTS/Dolby/AC3 to a more lighter stereo?
2) does plex transcode and stream only the audio track selected?

For the first question i assume changing the default of the streaming properties file.

Thanks in advance for reading and bothering to answer.