Hm, that’s interesting…do you have enough hard drive space? What options do you have checked?

Since I haven’t yet left for work, I opened up my 4K77 v1.4 in mkvtoolnix - if you just want the 35mm Dolby Surround track, here’s what it should look like (this is assuming you still want the chapter headings; unchecking the “3 entries” of “global tags” at the bottom shouldn’t cause any problems, but just to be safe I’d leave it checked:

Make sure you point your “Destination file” to the location you want that has plenty of free space (this file will most likely still be in the 55-65GB range even after most of the audio tracks are stripped), then click “Start multiplexing” and you should be fine. Just leave your computer alone while it works!