Nad m51 equalizer??

If I plug my computer in a m51(whit usb cable) is there there a way to use a tone equilizer directly in my computer?
Yes. The DAC is just recognized like a soundcard device. If the application you use to play music has DSP stuff (like JRiver), it will be run just the same before it gets to the DAC - though this is often not preferred as it won't be bit-perfect playback.