I can't speak for Handbrake but if you check the script MeGUI creates for downmixing you'll see this (5.1ch): the script I use goes like such:Д®ac3to.exe 'file.mkv' 2: 'file-out.ac3' -192 -48000 -down2 -down16 -normalize The entire world uses pretty much the same downmixing formulas, and eac3to is no different. I chose this over the MEGUI or handbrake method for the very same reason. if you have the original audio in AC3 or DTS (like makemkv gives) then you can use eac3to to do the downmixing for you to a 2 channel file with good results. If it's been downmixed to a AAC or MP3 aint much you can do. Hope this helps!Д®DIT: This won't help if your audio tracks have already been muxed down into (bad) stereo from their original source, but if you're getting a bunch of mkv files with mixed-down audio tracks, I'd check with my source to see where the mess is coming from in the first place. I've got several of these I use for various projects at home and at work, makes for *much* improved audio.

I'm not sure if it's cool posting direct links, but you can search on Amazon or Ebay for 'USB 5.1 audio' and you'll find a bunch of boxes that cost $15-$20 including shipping (USA) - they pretty much all use a C-Media CM6206 chip, easy to install, good support from C-Media. Makes for a much better audio experience. I've had this experience with more than a few mkv files - dialog barely audible compared to everything else going on onscreen - and I went the 'hardware solution' route myself: You can get a pretty cheap USB multi-channel audio device that'll output both digital audio (for an SPDIF connection) and analog audio outputs that let you plug your headphones or speakers into the center/front channel.

Audio volume low mkv files ac3 filter