The Kong, Before having done any modifications or tube rolling with the Steelhead, I would rank those 3 as follows: MP1>Steelhead>Janus. This is my Janus with upgraded coupling capacitors (using V Caps and polystyrene film and foil output capacitors on both the line and phono stages). The stock capacitors in the standard non-Signature Janus really drag down its potential, IMO. My MP1 is not stock, either. My only problem with it is that one of the modifications I performed was to replace the bottom tube(s) in the phono input dual-differential cascode with a bipolar transistor, as used by Allen Wright in his RTP3C. This gives the phono stage so much gain that it is unusable with all except very LOMC cartridges. Not a bad problem to have, but I cannot run it with MM cartridges. The Steelhead sounds very good with MMs in my basement system, as is.
Noromance, 6 Moons reviews are among the most unbelievable reviews to be found on-line, IMO, but I will take a look. There are several other reviews or posts on Audiogon claiming that this or that phono stage is also superior to the Steelhead; I don't let stuff like that faze me. The TEAD is solid state, is it not? I am still waiting to fall in love with any solid state phono stage. Many are "very good", to my ears, but all so far fail to reach that juicy musical Nirvana I perpetually seek.
I happen to have a stash of 6900s, but I use them in my amplifiers, two per chassis, and I am loathe to further diminish my supply. However, in the past I had come to believe that 5687s (the parent of the 6900) can sound just as good in audio applications. The 6900s are needed if you're building a guided missile, in 1965.