Atma-Sphere MP3 or something else?

hey all

some quick background. I'm a headphones guy but use speaker amps/pre power combos for my Abyss TC (and previously Susvara). 

current gear is
Primaluna Evo 400 preamplifier
Nad M23 power amp
speaker cables to speaker/headphone adaptor box (with 0dB and -17dB attenuation switch); i use 0dB for the hard to drive headphones, and -17dB for more sensitive headphones like Utopia etc.

i have the Atma-Sphere MP3 on home demo for a couple of days/weeks. had some initial issues with a faulty 12AU7 tube, but Ralph @ Atma-Sphere was great in helping me trouble shoot the unit. Am still having some background mild hum/electrical noise, very faint and only audible between songs/during quiet music or passages. not a big issue; am guessing either the inherent gain or from the rather old 12AT7 tubes.  if i flick the switch on the speaker/headphones adaptor box to -17dB, then the background hum disappears.

from my own listening, i really like the MP3. i think it outclasses the Primaluna evo 400 especially in the low end and mids. top end is less clear/sparkly than the Primaluna, but overall it makes for a very warm, inviting, lush sound. music and staging, pretty much everything sounds grander and "bigger" with the Atma-Sphere.

i'm looking to get a new tube pre. the Atma-Sphere seems like a rather "old" model. i cant find any recent reviews or forum posts about it. anyone here still using the MP3 or have the newer MP3.3 variant? is the MP3.3 an audible improvement over the older models? is it still a "relevant" component? i was also looking at the Modwright LS36.5 but the local dealer doesnt have a unit on hand, so i cant demo it, and it'll be a blind buy.