Volume of downmixed DTS and AC3 tracks VERY low

I use Plex Server (latest public release) on a Windows 7 machine and the client on the older Roku stick for all my kid’s media.

Everything was fine for a few years until mid-December 2016. I was using Plex Server version 1.2.7.2987 prior to this and all was running great and I upgraded to 1.3.3.3148 a few days after release, after which the volume became unbearably low for any files that were being downmixed from a DTS core track or a higher bitrate AC3 - it looks like anything above 348kbps has the low volume issue. None of my settings were or have since changed and to be honest, there’s little scope anyway to make huge changes to the audio on Plex Server, the Roku client or the Roku stick itself for my setup of the stick straight into the tv using stereo (2.0) audio. Files that I would have set the volume at around 25 on my tv I’m having to listen to on 85 to get the same volume so something’s definitely amiss. As has been mentioned in a few posts on various boards, it’s usually the case that surround effects nearly blow the tv speakers whilst dialogue is difficult to hear.

I’ve scoured Google, these and various other forums and there aren’t a huge number of similar posts however, there does seem to be a number of folks who have persistently been using Plex with this issue for some months.

Looking through the “Plex Server Changelog” on the Plex forums shows that there was a fix in the Plex Pass release of version 1.3.0 which reads “(Transcoder) Boost audio using a rematrix adjustment, instead of simply increasing volume. (#4594)” which I suspect may have something to do with it as this would have hit my system with the public update I did at the time and on the basis that all changes are listed, is the only thing that really could be linked to my problem.

Can anyone shed some light on this fix that Plex made or is this low downmix volume an issue for anybody else and is there anything you could recommend as a fix?