Downmix to stereo?

I'm completely new to this so bear with me ;P
I have a Panasonic TX-L47ET60Y and I've installed Serviio on my PC to stream vids to the TV. My problem is that for some strange reason videos with 6 channel audio are not properly downmixed to 2.0 stereo. They play perfectly on my PC but when I stream it to the TV via Serviio it's still in 5.1 mix even though I have the "Downmix to stereo" option ticked. So I hear some ambient sounds and music, but all dialogue is gone Example of a file that won't play audio properly;

Format : Matroska
Format version : Version 4 / Version 2
File size : 1.57 GiB
Duration : 1h 5mn
Overall bit rate : 3 436 Kbps
Encoded date : UTC 2014-06-16 02:14:32
Writing application : mkvmerge v6.0.0 ('Coming Up For Air') built on Jan 20 2013 10:28:01
Writing library : libebml v1.3.0 + libmatroska v1.4.0

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 5 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 1h 5mn
Bit rate : 2 984 Kbps
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.135
Stream size : 1.36 GiB (87%)
Writing library : x264 core 142 r2431 ac76440
Encoding settings : cabac=1 / ref=5 / deblock=1:0:0 / analyse=0x3:0x113 / me=umh / subme=8 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=18 / lookahead_threads=3 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=23 / scenecut=40 / intra_refresh=0 / rc_lookahead=50 / rc=crf / mbtree=1 / crf=18.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Language : English
Default : Yes
Forced : No
Matrix coefficients : BT.709

Audio
ID : 2
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : A_AC3
Duration : 1h 5mn
Bit rate mode : Constant
Bit rate : 384 Kbps
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Compression mode : Lossy
Stream size : 179 MiB (11%)
Default : Yes
Forced : No

Serviio automatically uses the Panasonic Viera (2013) profile for my TV.
My best guess is that my Tv don't support AC3 audio because a file using 2 channel AAC played fine. I have no idea how to fix the transcoding though (complete noob, looked at profile-file and it's all gibberish to me), so any eventual solution would have to be very thoroughly explained Any help would be greatly appreciated! Thx

[DenyAll]

What happens if you untick the down mix to stereo box? You may have to restart your PC to take effect.

Is this affecting all MKV files or just this one?

Thx for replying!
I tried checking "keep original" instead and it was the same. Since the file is in 6 channel audio that at least makes sense, but why would Serviio not be able to downmix the audio track to stereo if that option is ticked?

The problem is the same with every similar MKV files. They all use 5.1 mix and they all come out as such when streaming them, but when I play them on my PC directly they come out as a 2.0 stereo mix without any problems.
By comparison I checked the mediainfo on a different movie and that turned out to be in 2 channel stereo, which is why that one plays just fine even when streaming it through Serviio.

[DenyAll]

Well I suspect I know what is happening, if not why.

The "Downmix to Stereo" only occurs for transcoded media ie. if your media is being transcoded then the audio will be down-mixed to stereo during the transcode process, when this box is ticked. In your case, this file should be being streamed natively by Serviio to your TV using the Panasonic 2012 profile (so this box will have no effect).

When your TV receives the video natively with its 5.1 AC3 audio, the TV itself does the downmixing to stereo. So if my suspicion is correct and the file is being streamed natively, one of three things are happening:

• The TV is downmixing to stereo wrongly. Check the audio setting on the TV (try the PCM/MPEG one first); or
• The MKV has the audio channels mapped incorrectly in the source file (unlikely - it plays OK on the PC). Did all the affected MKV files come from the same source or same encoder?
• Serviio is remapping audio channels during the streaming process - never heard of this being the case, so I doubt it.

Some things to check:

• Play with the audio settings on your TV. Try resetting them ;
• If you play the movie from a USB stick on your TV do you get the same outcome? This would point to the TV rather than the media server.
• Try the Panasonic 2010 profile - this transcodes all MKV files. The downmix to stereo box should work. This is not a good final solution but is worthwhile for testing;
• Try playing via a different media server (eg. Windows Media Server - this doesn't do any transcoding).

<Edit>The above assumes you are playing the sound directly via your TV, not via a connected A/V unit?

Solution found!
I did as you said and played around with the audio settings on my TV while streaming the vid. When I got to SPDIF-settings and changed it from Auto to PCM (I have no idea what any of it means) stereo mix kicked in and we're a go!
Turns out it was the Tv that didn't downmix the audio track properly. You just saved me a ton of time and many headaches. Many thanks, kind sir.

Oh, and no the TV is hooked up to my reciever so the TV itself is turned down to zero. Profile still on Panasonic Viera (2013), Serviio back to "downmix to stereo" just in case. All is good for the moment, hope I don't run into any more troubles

Big thanks again friend!

[DenyAll]

Good to see it's working... but, you may want to keep playing with settings. The A/V receiver adds another element to the issue - you should be able to get it working with 5.1 so that you can enjoy surround sound (otherwise it seems a waste of an A/V unit )

My understanding: the TV will output either Dolby Digital Bitstream or PCM (stereo only) to the optical output. Auto makes the selection dependant on the source - AC3 5.1 will output as Bitstream while stereo will go PCM. So Auto is probably a better choice however then you need to set the receiver to decode the AC3. Mine does this automatically - it decodes Dolby Digital when it receives a 5.1 source and uses Pro Logic when it receives stereo. Have a play and see how you go.