Gumby is great, more analog than its big brother. On paper the Mjolnir 2 seems like a great amp. I needed the ability to drive speakers so I ended up with the Ragnarok - but I've always envied the tube option (oh yeah no longer) of the M-nir. It's got the power even for an HE-6. Enjoy!
Gungnir MB A2 is more neutral than even the Yggdrasil A2. I'd go for Schiit Bifrost 2 if you want to keep Gungnir MB A1's tonality