The very low impedence Denons (25 ohms) don't seem to mate well with the DV332. The mids/upper mids seem to have a slightly rough / hard sound. The rest of the sound is great - bass pretty tight, highs clear and detailed, great soundstage, etc.
Skylab reported to me that the DV337 sounds great with the D5000s.
And... I would guess the new Musical Fidelity XCAN v8, or the XCAN v3, would also, though they are tube hybrid amps. The XCAN v3 sounds good with the Grados (32 ohms).
The Singlepowers likely sound good with the Denons - they seem to drive the Grados well.
And the MAD EAR+ HD amps also likely sound good with them, since they are reportedly great with Grados.
I have used the GS-1 with stepped attenuator and I currently have the Rudisotr RPX-33 Mk2 and the RP7 Lite (hybrid). All of them match very good with my D5000 and D2000. There is not a big difference in the volume knob between the Ed9 and the Denon to sound at the same level.
The GS-1 is a little more analytical and dry kind of sound compared to the Rudistor amps. The RP7 has a better bass than the RPX-33 Mk2 IMO and with the new Beckman tubes I just put in it sounds wonderful.
I have a pair of Denon 5000's, love em. I think they are worlds better than my first cans, the K701.
The first amp I ran my Denons with was a Sound Quest SQ-84, it was amazing. I sold it and got a Blue Circle SBH because I wanted a pre-amp as well. Never got a chance to compare the two.
The SBH does a great job with the Denon's, but I still miss that Sound Quest. It was incredible. So dynamic, so much detail, so smooth. Midrange to die for.
Stephen at Quest for Sound is really, really nice to do business with. Unlike some exotic tube amp manufacturers he has a phone number - you can call and talk to him. He responds to emails. He'll give you a discount!
I just acquired opened Darth Beyers (!), and found I was happy with the sound on with my XCan V2 (6922 Mullards tubes) but not so much on my Total Bithead (voices and highs too much recessed, bass not blended enough)
As well, I am considering acquiring either the D2000 or D5000 for closed listening in the office, and would like an Amp with a DAC (I get my music off itunes/apple lossless from my pc) that can drive both the Darth and an upcoming D2k or D5k.
Previous reviews from Skylab seem to indicate Meier 2Move, Cantate (or Opera, although the price is a little steep) as good candidates for those 2 HPs.