External subtitles don't play

Hi,
I'm trying to set up a media server. I've managed to install Serviio successfully, and videos play on my DLNA TV. However, I can't seem to find why are external subtitles not playing. I've checked the "enable subtitles" case. I know my TV can play external subtitles as it worked with some other media server softwares (although they failed on other matters, but that's not the question). My subtitles have the same names as the movie files. I'm not sure I fully understand the log, but it seems the subtitles are detected (as seen on, for example, Clerks 2), but not used.
Any idea on what I am doing wrong?
Thanks in advance!

[zip]

I don't think the Philips supports external subtitles, without burning them in. Did you select that on the Subtitles tab?

Well I was trying Playstation Media Server earlier and the subtitles did work. Going to try the burn-in option, thanks.

[zip]

I assume PS3MS burns the subtitles in.

I tried the burn-in option and they didn't display, moreover it seems my computer couldn't follow the burden or the wifi is too slow. Well I'll keep plugging my pc with an HDMI cable!
Thanks for the help anyway!