PlugPayer and UPnP server always downsample in the chain to 16 bits.
The D7 sounds better with iPad + CCK + battery powered USB Hubs (note not any USB chargers pas data too, Y split cable eventually needed) than any USB port of a notebook/computer tested, and you've to mess so much with OSs settings to become crazy and it's nearly impossible to have a clean power feeding the USB Dac.
For the same clean power reason which attects sound quality, I've rouled out non battery powered USB Hubs.
With batteries you've also a portable (maybe not pocketable) system.
With iPad, without a portable storage wi-fi device able to 24bit perfect streaming (until now none confirmed working without downsampling), we're still limited by its internal storage capacity or by wi-fi coverage.
Look here if you're really interested in sound quality 24 bit-perfect portable configs with iDevices http://www.head-fi.org/t/625493/ipad-with-24-bit-files-high-storage-capacity-portability-which-configuration-works-without-downsampling#post_8667839 .
Edited by Thraex - 9/4/12 at 3:34am