You think 44.1K sampled music will sound better if played at say 96K? How does this work? Where does the added information come from? The mastering process has already dithered the file for 44.1/16 playback. You can't recover the data.
Ok If you want to try it go into the Audio MIDI Setup app and set you output device to a higher sample rate. The sound always comes out at whatever the output device is set to. You can't change an output device in iTunes because the output device is system wide.
A better way to improve sound for no cost is to ALWAYS leave all digital volume control sliders to 100% and then control the volume with an analog knob on the audio interface box. A digital control will reduce the dynamic range. (It has to do with the finite precision math used on al computers.)