Probably wants the 'official' codec, generally available on blu ray software like arcsoft, powerdvd etc..
Some good info here: http://www.makemkv.com/dtshd/
"The dtsdecoderdll.dll is part of Arcsoft TMT player software. So, if you are using Windows and have TMT installed, you already have the DLL - just set its path in MakeMKV preferences. If you don't have TMT installed, you can always download a free trial from Arcsoft website. Once you install the program, the DLL will be in program directory. You don't have to even run the program once. You may as well copy the DLL from TMT directory and uninstall TMT completely. If you use Mac or Linux, you may install TMT on a separate windows machine, in bootcamp or inside virtual machine, and copy the DLL from there.
If you don't have access to Windows machine, several internet sites offer this DLL as a free download. Just search for "dtsdecoderdll.dll" and you'll certainly find one. As mentioned before, MakeMKV will safely refuse to load any modified version of dtsdecoderdll.dll ."
edit: that's cool you have full usb 3 capability :) should be pretty fast to use that drive, almost as if it were another SATA drive.