
This is my gear 
I use the Earforce DSS for movies alone.
My setup for movies:
The optical out of my macbook pro goes into the DSS which creates 7.1 surround.
I use a stereo to RCA cable which gives me Left and Right analogue audio outputs which i plug in to the HDP's back.
Then i plug in my 650s to the HDP.
I tried the DTS demo disks with this setup. U571 bombing scene rattled the 650s(in a good way) when playing it over this setup(getting an immersive, speaker like sound which is good for movies). I also like the Kill bill fight scene with Gogo. and then the 'Behind enemy lines' scene where owen wilson dodges over landmines or something of that sort.
For music,
Source is macbook pro again. I play FLACs using VLC.
Sometimes i convert them to apple lossless and play them using itunes.
I use the USB/optical cable to connect to the HDP. My 650s plugged into the HDP.
As mentioned earlier, i need to turn up the volume to 3 pm (hdp in vertical position) to be able to drive the 650s in a decent manner. The sound is super clean. no noise, no hiss whatsoever. The bass is super tight and lean and also has improved extension. So is the evidence of increased soundstage and instrument separation.
Over 3 pm i can notice a slight hiss in certain types of recordings. if i play a silence wave file downloaded from brainwave.com i cannot hear any hiss even over 4 pm or the max volume but for general music, u can hear it for certain recordings.
if u play very low end bass over 3 pm, i hear cracks. esp for the u571 scene.
for rest of the music, i can use it slightly over 3 pm comfortably.
the amp section of the HDP is little under powered according to me(the consensus is also the same, so no surprises here).
I am not a treble fan and i dont listen to much of rock. I didn't notice any increased treble like others have mentioned. maybe i didnt notice that part yet by playing relevant music. or maybe as the 650s are slightly warmer in nature, i donno why, but, i didn't notice this one aspect yet.
However, i repeat again, the bass is improved in every way. The quantity and the quality. so are the mids.
These are some of my fav tracks on my setup:
Natalie Merchant's Tigerlily album,
Damien Rice - O,
Bowers and Wilkins Very audiophile new recordings,
FIM audiophile reference IV,
some tracks in David Chesky's ultimate demonstration disk,
Edited by Pradeep - 9/30/10 at 11:12pm