Sorry about the comments on the Pinnacle. I thought you were recommending it for the HE-6. Actually the reviewer preferred the sound of the HE-500 to that of the HE-6 with the Pinnacle for obvious reason: the Pinnacle could not drive the HE-6 properly but I do not think that the reviewer ever explicity acknowledged that fact, which steered many people away from the HE-6.
I own every single amp that I mentioned and have used them with the HE-6. I can assure you they can all drive the HE-6 just fine, and this includes the GS-X Mk2, which can drive the HE-6 at the high-gain setting. I never had to turn the volume up beyond 2 PM. However, if your DAC output does not have sufficient gain, then you may have a problem.
I did not make a judgement or real recommendation as to the sonic signature of various amps with the HE-6 as I believe this is a matter of taste. I had many listening sessions with friends at my place and some of them love the sound of the Dark Star and EF-6 with the HE-6. I myself could not stand it and much prefers to pair the HE-6 with the Woo WA5. I love this sound, which some of my friends detested, finding it lacking in attack/articulation (too slow) and way too colored/euphonic in the midrange. That was why I included in the amp list everything I own that could drive the HE -6, leaving it up to the readers to select the one they like through actual listening, which I strongly recommended. Buying an amp for the HE-6, or any high-end headphones based on someone else's advice, no matter how wise, is a very risky business that should not be considered unless there is no other choice.
By the way, when the EF-6 was used with Sophia Electric Magik Box ($2,500-ouch!) the sound improvement with the HE-6 was amazing. This combo outperforms the Woo WA5 in bass slam, micro details and macrodynamics, surrendering to the Woo only in sweetness in the midrange. For a combined retail cost of about $4,000 (compared to about $6,500 for my Woo WA5 with upgraded parts and tubes), that is quite impressive.
For that kind of money u can get urself an custom amp that goes one on one with the best of best...although without the flashy externals... for less money then those top of the bill amps costing 10.000usd or more mostly/partly of how they look...looks are sometimes most expensive part of the amp...my amp would be 1/3 more expensive it it would be totally of bruzhed stainless steel (both enclosures) and some other niftly exterior thingies the builder told me...making it look as expensive as it really was and look how it sounds...but i wanted simple..so i saved myself a small fortune..its solidly made...heavy and inside its only top stuff thats smiling at ya..as it sbould be...
But its ofcourse personal..many dont mind paying a cars worth for an amp partly because it looks absolutely gorgeous in their room..and they both do..dual mono wa234 and the viva...