Which Lamm should I add to the flock?

How much power do you need?
That will help you decide which model to get.
They have a SET with 18wpc. (ML2.1)
They have a standard tube model with 90 wpc. (ML1.1)
Then they have their hybrid amps with 110 & 220 wpc. (M1.2 and M2.2 respectively)

(I have the older M2.1 (200 wpc hybrid) amp, and I doubt I will ever upgrade amps again! Solid state like bass, with tube like mid-range.

If you were using a CA-301, (300 wpc, right?) I would guess you need the M2.2. (If you prefer a std. tube amp, the ML1.1 would probably work great too, and the M1.2 would proably work as well! Realize these later amps are a great deal less powerful than what you are used to using though.)
If it were me, I would get the M1.2, as it is pure Class A, but be warned, they run HOT. (The M2.2 also runs hot, but not quite as much.)

My two cents worth.

It is my understanding that your speaker is 89db effecient and rated at 4 ohms. I would say that the ML2 at 18 watts would probably not be enough. The ML1.1 at 90wpc would probably be pretty good as long as the impedence curve is rather flat. If the Tenors did well with you speakers I imagine the ML1's will also do well. The hybrids of course should have no problem with this speaker.

I would vote for the M1.2 Ref. I have been very happy. I wouldn't say they're HOT ... warm, but you can certainly always touch the fins on the side and the top. They do help keep my room warm during the winter, but do need A/C in the summer to keep the room bearable on the third floor of our house. Of course, the Tenors were my second choice, specifically the hybrids. But, unfortunately the company's financial situation scared me towards Lamm.

Best amp I ever heard was the hybrid 2.1. I heard a while back but I didn't get to hear the tube models. I agree with Kurt on that I just couldn't afford it.

I run my AA Capitole direct to Lamm M 1.2
The combination of tube and solid state is just fabulous
I asked Vladimir about changing to the ML tubes
I won't give his exact response but I still own the 1.2's
I've auditioned a lot of great amps None sound better to me than the Lamm M1.2