You can use fmit in linux and connect it to jack with qjackctl (or the cli). Also not sure what you mean by compatible? And what mixer is in question? I always thought that mixer was a piece of hardware. Although some can be controlled by software. But probably not the cheap ones.
Tascam us-1641. I don't think its technically a mixer, but as far as the PC is concerned its an external sound card. The programs I tried couldn't "hear" anything when I played a note, I assume that is because of the tascam.
I think you need to select what device to input from in the menu of the tuner. I used to use the NCH tuner free) with an Lexicon Alpha interface. Should be same with 1641.