Due to the incredible generosity of a fellow AC member, I was given the opportunity to try the Atma-Sphere MP-1 MK 3.1 preamp in my system starting late last week. The MP-1 will temporarily replace the very good Parasound JC-2 preamp and the remainder of my system stays the same (you can see the gear and a slightly out of date picture here:
http://www.audiocircle.com/index.php?action=systems;area=browse;system=711).
To cut to the chase, the Atma-Sphere MP-1 MK 3.1 preamp is nothing short of spectacular!! The easiest way to describe the preamp is that it takes the strengths of my system (midrange excellence, wide and deep sound stage, timber, tonality and texture that is spot on, and most importantly, the ability to engage and keep me engaged by letting the music be the star in its entirety) and makes it mo better!! It does this while improving at the frequency extremes and providing more detail and clarity, while sounding less clinical and mechanical. In short, with the MP-1 in the system, this is the best music I have heard to date in my room - period!
So what's the down side???
Nothing that I can find yet from the music side of the equation. In fact, I think it can get even better as the MP-1 is currently using the stock 6SN7 tubes. Luckily, I have a nice selection of 6SN7 tubes (NOS and new releases from Shuguang) that I will try in the coming days. It is also incredibly well built (I will try and take some pics and post them over the next week) and Atma-Sphere has been around for almost 35 years and provides some of the best customer service in the industry.
But (and this is a big but), this is not an inexpensive piece of gear.

It starts around $12 or 13k for just the line stage without remote volume control. Add some of the options that improve its sound and phonostage and this preamp pushed north of $20k! It also uses 18 tubes (8 12AT7's for phono and 10 6SN7's for the linestage) and is a two box design that will take up a good amount of real estate.
For those in the market for a state of the art preamp, this really belongs on your audition list. I am very happy to have the opportunity to try such an excellent piece of gear and I can assure you that I will be listening to my system as much as possible until it has to go back to its owner.
OBTW, even after removing the 8 12AT7's from the MP-1 (I don't have a use for the phono stage), I now have a total of 51 tubes in my system!!
George