Ultramixxer and FLAC files together with a controller ??

Hello ,

I am using the Ultramixxer with a lot of FLAC and MP3 files for over 3-4 years .
I would like to buy a controller …
Do i have to by afraid the controllers can’t work with the FLAC files ??
I think it’s not a problem , the controllers are only MIDI controllers ??

I have my mind set up on a Denon MC6000-MC7000 , or a Native S4

Greetings MArk