Wacom's 'Windows Ink' setting causes the tablet to send data in Microsoft's Realtime Stylus format. Unfortunately, Microsoft haven't implemented Stylus ID in RTS (if I remember correctly there's a partial implementation but it does not appear to have been completed). This means that you can't get Stylus ID data from your Cintiq when running with Windows Ink turned on. On top of that, the older Wintab standard doesn't support touch events fully so neither of the two systems are ideal.