Hey Syntax,
Actually, all of my friends that have listened to the aforementioned Lamm L2 reference preamp, believe it is "just a touch dark sounding". Notice I did not say it was "rolled off on top", as it is not that apparent unless one does a side-by-side comparision to another preamp, albeit another very high-end preamp! (Such as the aforementioned ARC Ref. 3, which is what I heard it compared with.) And again, it is highly musical. (I would not have recommended it otherwise.)
(BTW, you have a very impressive system, and those speakers are breathtaking to look at, so I can only imagine how they sound!!)
As an 6 year owner of the M2.1 amps, I am aware of their limitations, and one of which is that they, like the L2 reference preamp, is just a touch dark sounding. (And until I can upgrade to the M2.2 amps, (which fixed this very minor problem), I will happily live with it!) As I stated, Lamm products are very musical, and have a lovely sound. (To paraphrase the NRA, you can have my LAMM when you pry it out of my cold dead hands!) ;-)
However, Syntax does bring up an excellent point. The Lamm amps, and especially the hybrid amps, are excellent products for tube rolling. (The hybrid amps only have one tube in each amp, so tube rolling is "relatively" cheap.) I have upgraded from the stock Sovtek tubes, (which are just okay, and the sound is good using them), but going to a nice NOS tube can yield impressive results. Upgrading to something like the Amperex Orange Globe 6DJ8, will yield very good sound, and will cost less than $100 for the pair, (so that is a "no-brainer" upgrade, IMHO). And upgrading to something like the Amperex Pinched Waist 6922 will yield the ultimate in sound from these amps. Unfortunately, they cost at least a few hundred for a pair. (All of my friends, including myself have upgraded to the Amperex Pinched Waist 6922 tubes, or something very simliar.) One of the upsides to tube rolling, is that one can minimize the touch of darkness that the M1.1 and M2.1 amps have, so that one does not even notice it.