Springbok, if you look through the Atma-Sphere Owners Group web site, as I believe you have, you will find people there who believe the Atma-Sphere MP-1 is a superb preamp that is an exceptional fit to the A-S amps. They like the detail, transparency, neutrality and speed of this preamp. Also, they value the low impedance balanced connection that is supported between the two A-S products. Note that the key to this match is not just true balanced circuits, it is also the very low 600 ohm impedance for the connection between amp and preamp. Other preamps will have to connect at the MA-2s high input impedance setting.
That being acknowledged, other listeners have not found quite the same magic in the MP-1 when compared to other top competitors like the Lamm L2 and Aesthetix Callisto Signature. Differences I've heard commented upon are in low level detail resolution, dynamics (which is certainly not a problem for the MA-2 amps) and ultimate naturalness of reproduction of timbre (also not an issue with the MA-2s).
You ask about whether the Lamm is a truly balanced design. I don't know. But I'm not at all sure that being balanced should drive your decision. All of the Aesthetix gear is truly balanced, but I am running my Io via it's RCA outputs into my A-S MA-2s with excellent sonic results. (Of course I do want to try it on balanced interconnects, but that requires obtaining an identical interconnect cable terminated with XLRs to accomplish.)
As to the BAT, many people certainly admire this preamp, but, imo, the Lamm L2 and the Aesthetix Callisto Signature are in another league. For my listening priorities (which may not be yours!), I would consider the Aesthetix Calypso linestage before the BAT; the Calypso delivers a naturalness in rendering the timbre of instruments and harmonic overtones that the BAT simply misses to my ear. Also, the Calypso easily will give you all the flexibility and user convenience via remote control that you liked in the Mark Levinson, plus more.
As you note, what you are trying to determine is not easy; it is very difficult to be able to hear much of this gear, let alone hear it under any sort of conditions that allow one to differentiate what one is hearing from which component within the system.
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