nuforce Icon HDP as PC source ?

Yes it should work right out of the box just plugging it into a USB port (or powered hub) with your W7 x64 machine.  W7 will install the driver automatically.  Then you just need to either change your default audio playback device in W7 to the HDP or you can just select the HDP as the output device in your media player(s) of choice (or both).  Then plug your headphones in and enjoy.  Btw, it gets a lot better after about 300 hours or so (at least mine did, along with my HD650's.

You might want to use WASAPI exclusive mode with your audio player to get the best possible sound quality output out of the HDP and W7.  You need to use an audio player that has support for WASAPI, usually in the form of a plugin.  For example, there is a WASAPI plugin for Foobar2000.  So you would install the plugin in FB2k and then select WASAPI ICON HDP in the output section of Foobar and you are once again good to go.  WASAPI enables your player to output the audio stream directly to the HDP w/o the W7 mixer or other PC audio interfereance getting in the way.  Usually results in improved SQ.  For me, WASAPI got rid of some occasional audio glitches the HDP was picking up from my computer.

The HDP will automatically adjust to everything.  But you should select 24 bit output data format in your media player assuming it has that option  (Foobar does).

The easiest way to use the HDP for everything is just to change your default playback device to the HDP.  Then all your audio will go through the HDP, and you would set your computers volume and media players volume to max or 100% and then control the sound level with the HDP's volume knob.  You would probably want to run your speakers, assuming you have them, from the RCA audio outs on the back of the HDP.

Note that when you plug a headphone into the HDP's headphone jack, the HDP's RCA outs will automatically shut off, so can't listen to speakers and headphones at the same time through the HDP unless you run them both from the HDP's headphone jack.

The HDP should continue to work with future Windows OS's for a very long time to come.

Enjoy your HDP.  I am loving mine.

It's played everything I've thrown at it fine, all automatically, including movies, games, audio of various bitrates.  I believe it has some kind of USB "receiver" or "converter" chip that I currently forget what it's called but it's function is to receive the USB audio stream and take care of any adjustments that may need to be made, all seamlessly without need for any user intervention. 

This subject is discussed a bit in the main review thread for the HDP on this site so if you want more info about it, you might want to read through that rather lengthy thread, but most of the important stuff is in the first post or two.

And, it sounds just awesome, especially with lossless material like FLAC files, assuming you also have headphones or speakers worthy of it.  It generates the best sounding audio I've ever heard though my HD650's, but those are the best headphones I've ever listened to so far.  My modest rig (consisting of my W7 laptop plus the HDP plus the HD650's) just keeps sounding better and better the more hours I put on it.  I'm a very happy camper ever since they got more or less burned in.

The only thing I don't know if it really does (or how it does it if it does) is handle multi channel output beyond simple stereo (as I only use it to output stereo and it only has two channel output i.e., the two RCA outs (L & R) and the stereo headphone jack). 

But anyway movies through it sound pretty darn good to me without taking any special measures.  I use Daum Potplayer for my video player and it has very good built in audio processing that just works w/o the user having to mess with it, although you can dig into the settings if you want to.  I guess most of that stuff is probably handled by the media player's audio codecs which probably downmix that kind of stuff to stereo before it even gets to the HDP.  But not really sure about all that.