...but with files containing 2 audio streams, only one steam is visible
Yes, when a file is transcoded by Serviio only one video stream and one audio stream is transcoded. All other streams are dropped.
The only way to support multiple audio streams at the moment is to ensure the file isn't transcoded - use a tool like MKVToolnix to change the order of audio streams so that the first stream is one that doesn't need transcoding, or use a tool like XMedia Recode to add an audio stream (as the first audio stream) that your TV supports (eg. AC3).
Also, now videos are still being transcoded, which are not needed to be
Cant see why the example you provided would be transcoded. Are you sure it is? Check your subtitle settings.
but the aspect ratio is messed up.
yep, a known issue for Panasonic TV's (and others) ignoring aspect information on transcoded mpeg-ts files. You can overcome by moving the line:
<Matches container="matroska" vCodec="h264" aCodec="dca" />
directly under the line
<Video targetContainer="mpegts" targetVCodec="mpeg2video" targetACodec="ac3" aBitrate="384" DAR="16:9" forceInheritance="true">
This will transcode the video as well, padding it so as to reproduce the original aspect ratio.