The only headphone I've driven out of the Rag 2 so far is my HE-6. I'm one of the first HE-6 owners, and it's the first time I've liked it out of any headphone port. I used to drive it with speaker amps to get it to work right. Now it works right out of a headamp! I did try them on gain 2, and they lost body/dynamics but still sounded pretty good, almost stat-like. The way the Rag 2's volume works, gain 3 still leaves a wide power curve on the knob. Gain 3 seems to be required on all speakers, even bookshelf. I use it a lot with speakers. I haven't tried gain 1 yet, I'll get some other cans going soon enough and report back.
I'm guessing that using gain 2-3 with the HE-6 is analogous to using gain 1-2 with most other headphones. Haven't used gain 1 at all so far.
I only had my Ragnarok 2 for 11 days. I decided to bite the bullet and sent it back yesterday under the 15-day thing to get the 'just an amp' version, and am really missing it. But I want to get it right for my needs. I was torn when I bought it, and made the wrong call. If it was going on a desktop with a turntable, the 'fully loaded' version would be the way to go, but mine's going to be in the living room. Yeah I do stupid schiit sometimes, but this lets me consider a temporary detour to Yggdrasil GS. Of course my goal is to end up with both of them, if I manage that it's going to be a merry holiday season indeed.
I'm going to a meet next weekend and there will be a Rag 2 there. I've had the Rag 1 for 3.5 years. It's very good, in particular the 4 watts of Class A power. Still the heat it operates at has me concerned about longevity. I assume you are using the XLR connection for the HE-6s. I borrowed a set and like them at Gain 2, but there wasn't much spare room on the knob. If i sell my 1 and get the 2 it would as integrated only. I have a pair of speakers that are 96 watt/db/meter - they like gain 2, I have a pair of old monitors that are 86 db/w/m - gain 2 is good for background.