I hate to introduce another choice, but I have to: the Audio Technica ATH-AD2000. I asked my twenty-something niece to burn me a rap CD I could "get in to", and she did -- very mainstream stuff, Jay-Z, Kanye, fiddy -- 20 random tracks, I really loved it.
I didn't bother with the Orpheus, a non-starter. So here is the list of what I tried over a two day period -- the DAC in all cases (except the beyer amp, which has the DAC built in, and the RWA Isabellina, also has its own DAC) was the one built-in to the Wadia 781i, which has rolled off highs no doubt. I will try again with the Benchmark, but I wanted to post first and take the flames.
O2 Mark 1 and O2 Mark 2 (Spritzer Mod) and Baby Orpheus HE60s driven by Kerry BHSE and 717 and SRM 1/Mk 2 ... all combos ... NOT the right choice. Too smooth, no raw. Need raw for this music to work.
T1's -- excellent. 880/250 and 880/600 ... sounded the same as each other, slightly less detailed than the T1's. Listened both off the beyer amp and my QES special-built for beyer phones.
HD800s' -- totally the wrong choice for this music IMHO ... why would we tell the OP this is a rap phone? It's just not. Better listen to it before buying. Tried with a Beta 22 and a Head-Direct EF1 with a tung sol -- both amps voiced orginally for the HD600 so I though this should work. Didn't.
GS1000s -- Terrible. Unlistenable. I replaced the bowl pads with flat pads so this could be my fault, but I thought on other music the headphile flat pads improved the sound. Just awful.
button RS-1's -- much better, a contender.
K1000s (using a RWA Isabellina optimized by Vinnie for the K1K's, using the HiRez Wolfson DAC) -- really really great.
K701's with an M^3, Beta 22, and EF1 -- excellent, a contender.
Dennon D2000s and D7000s off the same three amps .. OK, nothing special.
AHT-AD2000. OMG! Now I was "in the club". Visceral, real -- the music worked. There should be federal and state statutes that prohibit a 62-year-old fat white guy from dancing to this stuff, but there ain't, so I did.
The final box score IMO:
AD2000 > K1K > RS-1 > T1 > K701 > 880s > Denons. Failures: HD800, GS1000. Wrong Concept: Stax and Orph.
I am prepared for the flames. I am sorry that I had no Ultrasone to try ... Dev's got my Pro 750s. I bet Ultrasone would have done well. And I forgot to try the HF2's ... maybe when I switch DACs.