Converting to HEVC without loosing any streams and/or quality

[Hazuzi]

I have a movie in 1080p and an mkv container
Summer Wars by the Anime Sub-Group CoalGirls
and I would like to convert the movie from >9GB mkv file to an HEVC mkv file, but it has 2 audio streams and 2 subtitle streams, which I would like to keep, I have tried to use Wondershare Video Converter Ultimate, but I cannot for the life of me figure out how to do that.

I would also use a different program if that is necessary.

Please, oh wise and polite video helpers, lend a hand to this humble soul in need

Edit: Would it be possible to simply convert the video and then use a tool like mkvtoolnix to "merge and purge" and make a desired file?

[LigH.de]

Converting without losing quality, but using a lossy algorithm, is generally not possible.

Converting without noticeable loss (= "visually transparent") may be possible; but don't expect the result to be still smaller than your existing video. Your video was already compressed, it contains compression artifacts; recompressing it without making such artifacts more ovbious may require more bitrate than before.

So, apart from the annoying theory...

It will probably be possible to recompress the video to HEVC, using capable converters like MeGUI, Hybrid, StaxRip, Handbrake ... and then exchange the video stream (removing the original video stream and inserting the HEVC copy) using MKVtoolnixGUI.

If this doesn't work, there may still be a way to extract all other streams and re-multiplex them around the HEVC video. Still, the mkvmerge package will have the primary tools to handle the MKV container.