Hi Saturn
Not exactly. Tubes like a resistive load. A resistive load is characterized by a flat impedance, and an inductive rather than a capacitive phase angle. Tube amps tend to do better with speakers which do not make large current demands on the amp by swinging from 8 ohms to 2 ohms and back again. Gradual impedence changes are easier for tube amps to drive. Tubes like a steady load - capacitance is the opposite. When a speaker behaves in a capacitant manner, it presents an uneven load to the amp, asking the tube amp to put out large quantities of current in a short amount of time. Speakers which make such demands on amps are not tube friendly.
Therefore, what makes a speaker tube friendly is not whether it is rated at 4 ohms or 8 ohms, but rather whether the speaker's impedance is relatively flat and consistently hovers around 4 ohms, and if the phase angles are more inductive than capacitive.
Same for efficiency ratings - if you look at the graphs of some speakers rated at 8 ohms you will see that they are measuring less than 4 ohms for much of their fr curve.
Stereo Times has a review of the Dynaudio Audience book shelf speakers - a very tough load for a tube amp, a very demanding load for a solid state amp!
http://www.stereotimes.com/speak081604.shtm
Martin Logans and Maggies like really powerful solid state amps.
The M3Ti is an extremely tube friendly speaker. I think part of the reason for this is that there is no cross over between the amp and the driver, the simple cross over is hooked to the tweeter only.
The Triangle Celius is a wonderful speaker, very tube friendly even with the ASL 5 wpc MG S1 15 SET amp.
I haven't A-B'd my M22 like Michaura M55s with tube and solid state, but I had 2 set up with my 5 wpc tubie and have 4 M55s in my office system. The front 2 are driven by a Yamaha M80 gentle BRUTE of a 250 wpc 2 channel amp - the side surround pair driven by a 100 wpc Onkyo M282. I listen to mostly music on the HT system. I love them both, the Yamaha is an exceptional amplifier and makes stunningly beautiful music. But for kicking back at the end of the day my favorite system for music is the 2 channel tube system.
