For Epic Piano, you need a Full Kontakt Version (Retail Version). Free Kontakt Player won’t open it (or it will give “Demo” notification). You need a 5.1 or higher version of Kontakt Retail version.
You can also see this system requirment information on the product page: https://www.noiseash.com/epic-piano/#specifications
Since Epic Piano Instrument is a standard open-format Kontakt library, so you can only load and browse its contents by using the normal “Files” and “Database” views in the Kontakt browser. You can also use the “File” menu button at the top of Kontakt. The “Libraries” tab in the Kontakt browser is only designed for locked “Powered-By-Kontakt” Player libraries. That is a design limitation that Native Instruments decided on in Kontakt.
The “Add Library” feature of Kontakt was designed to work exclusively for “Powered by Kontakt” player libraries. That’s just the way Native Instruments designed Kontakt. You can still quickly browse and load the Liberis Instruments folder using the “Files” tab or by adding it to the “Database” tab in the Kontakt browser.
The advantage in making our libraries open-format instruments is that you have direct access and ability to edit or manipulate the .wavs, which is very important to a lot of users. You also don’t need a serial number or use “Add Library” to install it. It’s ready to go as soon as you install it and you can use it on any number of computers you own simultaneously.