Quake 1 Matebuntu 15.10 64-bit, game disc mounts as audio cd.
 

Hi, trying to install the original quake off the actual install CD, but I can't figure out why the disc only mounts as an audio CD on Linux where it mounts properly as the game install CD in Windows.

mount it from the command line. Open a terminal and as root run

mount -t iso9660 /dev/sr0 /mnt/cdrom

/dev/sr0 should be your drive path but it might be different on your system and /mnt/cdrom is where I mount it you can use another directory if you want.

I assume you are going to use a native linux quake client like darkplaces? The only files you need off the disc are the pak files. Once you have mounted the disc with the command above, from the command line change to the directory or open your file manager and go to the directory, you will now be able to view the files on the CD. if its an original disc like I have you will have to extract the pak files from the resource.1 file. Copy the resource.1 file to your /tmp directory and then extract the pak files with this command

lha e resource.1

now you have the pak files under id1 directory.

See here from some more information http://tldp.org/HOWTO/html_single/Quake-HOWTO/#ss2.1

This is what I get when I try to mount from terminal.

that's because you don't have a directory called /mnt/cdrom. Like I said above you can use any directory you want. Make a directory in tmp like this "mkdir /tmp/cdrom" then run the same command but instead of /mnt/cdrom use /tmp/cdrom