Tube-friendly speakers

You might also want to put Gallo Ref3's on your list. I drove them fine with 50 tube watts, and they have a planar-type sound.

Roblanger, all the Vandersteen 2 varients are tube-friendly. I know the Dali Mega-line is but I am not familiar with their smaller models.

Tvad, in the case of the Merlin, the impedance swing is well within the capabilities of almost any tube amplifier, even our S-30, which can be quite sensitive to lower impedances. I don't consider 6-8 ohms to be challenging for our amplifiers at all- that sounds easy to me.

As far as 'high enough'... this has to do with the maximum power transfer of the tube amp in question, which is usually a function of the output transformer and the load of the speaker. For example if you load the 8 ohm taps of a tube amp with a 4 ohm load, the load presented to the power tubes by the transformer will be significantly less than the intended design- the amp will make less power. In some cases it could cut it in half. A speaker designer can take advantage of this phenomena in crossover design. I think a classic example is the old Wilson Watt.

The Watt had a reputation for being detailed but bright in the old days. This was because of a tweeter resonance. Wilson had a substantial trap that measured about 2 ohms at the resonant frequency of the tweeter. When you put a transistor amp on that, the amp simply made more power to deal with the 2 ohm load. So this did exactly the opposite of the intention of the design. But when you put a tube amp on that same load, the tube amp made no power, thus preventing the resonance from being a problem. IOW, the reputation of the speaker came from transistor amplifier users, not tube amp users.

Once the inpedance of the load is high enough, the amplifier will exhibit a sort of 'constant power' phenomena- it will be a slowly decreasing amount of power as the load is increased; the power curve looks a lot like an airfoil curve in profile. With OTLs the effect is increased; once above the maximum power transfer point the load can be tripled without significant power loss. All that is required of the speaker designer is to understand that this phenomena occurs, thus my paradigm conversation:

http://www.atma-sphere.com/papers/paradigm_paper2.html

My Rogue Audio Cronus integrated amplifier (55 wats of EL-34 tube power) does an absolutely wonderful job driving my Vandersteen 1C speakers. The Vandersteens may indeed get along quite well with your AES Six-Pac amps.
Good Luck, and Happy Listening.

Spendor,Reference 3A, Gallo, Harbeth(3s)

My 45 Watt Cayin A88T drives my Spensor S8e floorstanders with authority and ease. Interestingly, the S8E with its strong bass and thick midrange 8" woofers, demand less power for a similar moderate sound level as did some smaller Spendor 3/5 monitors. The Spendors can be played loud without distortion with 45 tube watts.