I'd do it the other way round for safety reasons. Having that master volume knob maxed out will mean that if your computer output levels are changed, then you're gonna burst your eardrums when that blasts you. Also, not everything gets routed through the master volume in windows (e.g. recording software via ASIO).
Your UX2 is a soundcard, it will play back all windows sounds; not just POD Farm - keep that in mind; you don't want to have to adjust each program e.g. window media player, itunes, pod farm to control the general output level. I have the output set in pod farm to 0dB. I then adjust the output on the device to a reasonable listening volume.
Hope that helps.