I tried this: PWMDAC - Open Music Labs Wiki
it works but i don't know how to get the values and send it back to the other arduino (via RF).
Maybe i would start with the converters and then see what i can do after that.
But anyway, when i have the converters, do they give me the negative and positive range for the audio wave? Or i have to trick them out with a resistive voltage divider and a capacitor?