The hard part of having a large computerized library is software. Dedicated high end solutions have proprietary software. PC have lots of media player software but they drive output from the PC. Slim is open, but media player software does not allow you to direct to a Slim device for output. The Klimax DS would be just perfect for me (I also own plenty of HiRes downloads) if it enabled me to uncouple the software player interface (PC) from the data (NAS) and the DAC (KDS). Linn says they support PnP AV 2 standards, but what media player software supports that? I use JRiver, AlbumPlayer and Helium (mainly for metadata management). Where can I find listings of media player software that support directing the stream to a PnP AV 2 device? Linn's site does not do this, nor pnp.org. If the software supports it, then the Klimax looks like a winner to me. Where is the software?
Within the architecture of uPnP, there are MediaServer, MediaRenderer and Contol Point devices. In this architecture, the decoding from various file formats (FLAC or WAV for the Klimax DS) to PCM followed by D/A conversion occurs in the MediaRenderer device. The Control Point allows browsing of content and creation of playlists at the MediaServer as well as control of the MediaRendering device to stream and render this content from the MediaServer. Linn provides an application that runs on what they describe as a "hand-held wireless touchscreen" that delivers the control point functionality. The images from Linn show this wireless touchscreen to be a Samsumg UMPC.
A quick Google search for "media player upnp" turned up On2Share that promises:
"With On2Share Pro you can also broadcast your music and video files to UPnP Media Renderer. This solution is also integrated into Windows Media Player. Once you play a audio or video file in your local WMP all UPnP media renderers of your network play the same file. Additionally, On2Share Pro includes an UPnP AV Media Renderer to access these broadcasts on your network."
Sounds like that is the tool you're looking for. Using On2Share you should be able to use WMP to select an play content on any uPnP MediaRenderer (e.g. the Linn) on your network.