You can convert ESX24 libraries in Kontakt 5. Unfortunately I have read that this feature broke in Kontakt version 5.2 and it will crash your DAW if you try.
There is, however, still a way to get this to work. I’m afraid I only know how to do this on a Mac:
In order to enable the EXS24 to Kontakt conversion feature again you will need an older “kconvert.bundle” file. This is the file that does the converting and in later Kontakt versions it contains a bug.
If you have Kontakt 4 then you can find a working “kconvert.bundle” file in:
Just login and type Kontakt in the search field, then find “KONTAKT 5.1.0 Mac OS X Update”.
Once downloaded do this:
1. Expand the “Kontakt_5_510U_Mac.dmg”.
2. Right-click on “Kontakt 5 5.1.0 Installer Mac.mpkg” and choose “Show Package Contents”.
3. Navigate to Content>Packages, Right-click on “Kontakt 5 System Extensions.pkg” and choose “Show Package Contents”.
4. Double-click on “Archive.pax.gz”
5. A new Finder window should open up (in your Downloads folder) with folder “Native Instruments” and in that folder is a Kontakt 5 folder. In there is the file you need called “kconvert.bundle”.
6. Navigate to: HD>Library>Application Support>Native Instruments>Kontakt 5 and back up the newer “kconvert.bundle” (version 220.127.116.11) by copying it somewhere else.
7. Copy/replace the older “kconvert.bundle” (version 18.104.22.168) into HD>Library>Application Support>Native Instruments>Kontakt 5
Then it is simply a matter of dragging the EXS file from the Kontakt browser window into the Multi window. It should load and then you can save it as Kontakt instrument.
If you are on a Windows machine then it is worth trying to see if you can import EXS files.