My personal favorite alternative for the 6N1P (the shorter ones in your Valhalla) are the Genalex Gold Lion E88CC/6922, they are around 110 American Kopeks for a low-noise-plus-triode-balanced-plus-gain-matched pair. Have yet to find an E88CC (or compatible) that sounds more euphonic to my ears. They sound great in the Valhalla, and they elevate my Mjolnir 2 to a wholly different level (compared to the GEs that mine came with from Schiit, at least.)
I'm also not averse to the JJ E88CC/6922 Gold Pin, they clock in at around 65 for a low-noise-plus-triode-balanced-plus-gain-matched pair. But they don't come close to the Gold Lions, in my humble opinion.
As to the 6N6P, the longer ones, I'm not even sure there are any alternatives worth mentioning to the ones that came with your Valhalla. But I've only ever done some cursory research on that type, so I might very well be wrong.