If you want a very dark sound but mostly due to low noise, get the DV336se.
If you want a really rolled off top end, get the LD MkII, not the MkIII.
But that's only guaranteed for your HD650 since OTL amps can react differently to low impedance loads. My MkII made a K701 sound like a tin can with barely any bass (and what bass lines and double peds was left was a mumbling, barely audible mess), basically making it even worse and farther off from the HD600, while boosting the low end on my SR225 (not that it was very clean and controlled bass like the HD600 on a Violectric or Meier amp; yes, even on the high impedance headphone, the MkII or even the MkIII wasn't totally that clean in reproducing fast bass) and making it an HD600 with even worse imaging vs the K701. Not to mention that OTL tube amps deliver the most power at 300ohm and the lowest output at 32ohms, and there are more low impedance headphones with lower sensitivity than the high impedance Sennheisers and Beyers.
If you want one that works just as well with your Sennheiser and lower sensitivity HiFiMan, but you still want a dark sound, skip even the Lyr and keep saving up for a WooAudio WA22.