Hey, USAudio. Here's my response to your email:
I like the m902 with the HD650 (w/Cardas cable) for nearly everything. The clarity, definition, quickness, soundstage are the best I've ever heard. My primary listen is:
lossless tracks on my computer > Foobar2000 > USB > m902 > HD650
But for rock with lively bass, e.g., CCR's "Have You Ever Seen the Rain," I like the GS1k (w/ Black Dragon) in the lineup. It's a lot more musical, warmer.
I only got the m902 recently. Until then, the HRDB (maxed) w/ stock HR balanced cables and HD650 was my first choice.
Before the HRDB, the HRD-SE (maxed) was it.
With the HRDB, you should definitely get the DPS ($399). The difference between the DPS and the Astrodyne is significant to the point where the quality of the HRDB sound is compromised without the DPS. I don't understand why HR even bothers with the Astrodyne.
Now for the tough part: Which is the best combo? For pure musical enjoyment, I'd say the m902 and GS1k with an aftermarket cable. (I've never tried the GS1K with the stock cable.) For an analytic listen, to get into the music, I'd say the m902 and HD650 w/aftermarket cable. You hear everything, accurately.
The HRDs are warmer in comparison to the Grace, and I suspect many prefer the warmth to the clarity. For my ears, once I heard the m902 and all that it reveals, I have difficulty returning to the HRDs. In a direct comparison, the HRDs seem fuzzier, less accurate.
I'm not sure if I'm just in a honeymoon stage where the latest sounds best only because it's new and different. But for now, the m902 is my first choice.