Player doesn't supoprt Dolby Digital Plus (eac3), can't get Plex to transcode



Sorry for the double post. I posted this earlier in the QNAP sub-forum, and it seems like this is a better place to ask this.

So I have an old Popcorn Hour A-210 connected to an even older TV, and I have a 720p mkv file that has Dolby Digital Plus (eac3) in my media library on a QNAP TS-251+. The video plays fine, the problem is there's no audio.
Oddly, according to the log, Plex is using the Generic profile, although there's a Popcorn Hour profile. The Popcorn Hour profile says eac3 is supported by my device although it's not.
So I'm trying to force Plex to transcode but I can't get it to work. as a hack, I tried replacing the generic profile with an edited Popcorn Hour profile (obviously, when Plex Server was down), removing the eac3 support but that didn't work.

the documentation ( didn't help much.
as a side note, where are the USER profiles stored?

Would appreciate any suggestion.
btw, the H/W should be powerful enough to transcode on the fly.