I think you're on the right track with the RCA to 1/8" mini plug into the Focal Speakers. I would be surprised if the Focal System had an internal DAC, but I'm not familair with them, and actually it wouldn't matter because by using the RCA mini, you will effectively be bypassing any internal DAC anyway. However, just because a speaker system accepts USB, doesn't mean that it has an internal DAC.
Rich
Rich