I'm also with Mitch4t. While not essential for me, a digital in will allow me to listen to Internet radio and other digital sources and possibly eliminate an extra DAC in the system. The HAP-Z1ES DAC, while not the best out there, will probably be good enough for me. The tube stage mods being offered by Vinnie and Dan may take it to a whole different level.
The HAP-Z1ES is not being targeted at people who already have a computer-based audio system. Their target is someone like me who has songs stored on computer but hasn't gone to the lengths of installing the different drivers necessary, buying an external DAC, installing a media player like JRiver, etc so I can listen to it in my two-channel system.
Do I forego flexibility and processing by not choosing a Mac/PC/DAC combo? Yes, but I also eliminate endless fiddling around with the computer audio system.