It was my favourite amp at the first national with my K340s.
Also, you could try the 6BQ7A/6BZ7 in place of the 6922 as it is basically just a higher gain, cheaper, and some say better sounding version of that tube.
Not sure about the Luna, as I didn't try it with Grados, but my amp is just fine with Grados and K340's and only has 24 steps.