Output impedance is what damping factor is about, IOW it is the ratio between the output impedance and 8 ohms. However measurable, it has hardly any effect on the loudspeaker, unless we are to believe that a speaker displaced is to stay that way when the voltage is removed. Of course that notion is fanciful- the speaker returns to rest. Damping caused by the amp has no effect as the amp *at any time* is producing a voltage that causes the speaker to displace to a specific location with respect to its motor (magnet or ES field). Thus: Damping factor is a popular myth, an urban legend that is made up.
As far as Halcros being perfect?? Sorry, but they are far from it! I can run a demo anytime to dispell *that* and did so at THE Show in Las Vegas, where they were two doors down with the same speakers we were running. The differences were thus very apparent.
It is a rare speaker that does not sound better with tubes, although some will exhibit compromise in some areas (Which are always issues of load impedance). IOW tubes are better sounding in general than transistors in general.
It sounds like you need to hear a set of the MA-2 MkIIIs, which you did not hear when you made your comparison. You must not have played material with bass, else you would have noticed that the Warners weren't making what they should have on the Sound Labs. I suspect you like things brighter than I do, which the Warners would have been. Sound Labs do that with transistors. Its they way they work.
I think you do not understand the 'current issue' but don't this is not an attack- this issue is generally misunderstood :/
Here is what is happening in audio today: There are 2 paradigms that are in conflict. One is the Voltage Paradigm and the other is the Power Paradigm. In the VP, it is assumed that the only thing that is important to measure in amp and speaker specs are voltages. This is the reigning paradigm. OTOH the PP assumes that it is important to measure power response, not just voltage. In this camp, (knowingly or not) are ESLs, magnetic planars, horns, single driver speakers and a variety of box speakers; all which sound better if used with an amp that will make the same power regardless of impedance. SETs and other zero-feedback amps fall into this camp. SO- our amps may have 'current', but only in the context of making Power, without the price of feedback, which increases odd-ordered harmonic content so objectionable to humans.
Magnaplanars can have amazing performance for the price so it is important to winnow that out of them. If you need shear volume, you may have to go solid state, but for nearly everything else, tubes rule.