How many tube watts for Vandersteen 2's?

Maybe it was breaking in? I would try the 4ohm tap one more time after it has broken in for a while and you use to the sound of the amp. I'm curious what you think then. A great little amp - isn't it?

I don't believe that light loading the RM10 would reap any benefit while driving the 2ce either, particularly if it sounds better from the 8 ohm tap.
The choice of tap may very well be speaker dependent however,the 8 omh tap has been the definative choice with each and every speaker speaker I have paired it with.
Tannoy Westminsters, Merlin VSM,proac 2.5, and a pair of vintage quad 57's.

Ecclectique, any idea why that would be given Roger's comments on the benefits of "light loading"?

Hi Pabul57. I am not sure about Rogers comments with regards light loading however,it is impossible to ascertain with any certainty which tap is appropriate to use as no loudspeaker represents an unchanging impedance at all frequencies.
The 8 ohm tap typically match loads between 4 and 8 ohms, the 4 ohm tap will be a better match for impedances that fall below 4 ohms.

The one thing that I am more than certain of..... The 8 ohm tap is far and away the right impedance choice for the Merlin.

If you use the 4 ohm tap on an amplifier with a speaker of higher impedance, the output transformer will be inadequately loaded, and so it will express less of its winding ratio and more of its inter-winding capacitance. This can result in the amplifier no longer having flat frequency response. In addition, the transformer can 'ring' if inadequately loaded, which is another way of saying that it will distort.

The Merlin is an 8 ohm load, with a dip to 6 ohms or so. Its a benign load and an amplifier with an output transformer, if the transformer is designed properly, will likely work best on the 8 ohm tap. This will minimize the artifact of the transformer.