Best speaker for medium to low power tube amps??

Coincident work well.If you like the Merlins the Super Eclipse will be a nice choice also.

the guarneris are lovely...warm,open,transparent and non-fatiguing sound with excellent midrange. they won't give you deep bass though. they sound great with tubes amps like ARC,Graaf etc. they are not that difficult to drive ...about 87db although with more powerful amps you will get the sense of ease with the way the sound is produced.

The new Audio Physic Virgo would be a nice choice. In a room your size they would like 50w or more I'd imagine. Check out the Immedia site for set-up instructions.

2nd of the Virgo's. Either version. The new ones are better, the old ones are a steal used! BAT VK60 makes a nice match.

I got mine from someone who had been driving them with a 50 wpc tube amp in a room about 12 x 15. He had been very happy with that combination. ( Sold because of low WAF for multiple systems. ) Other sources have also been happy with the Shearwaters ( 88-89 dB/W sensitivity ) combined with tube amps in that power range.

I myself am using a ss Celeste W-4070se ( about 70 wpc ) with my Shearwaters There is gobs of power for my 15 by 22 room.

Another possibility might be Reference 3a. The DeCapos are rated at 92 dB/W. I heard them do very well with Antique Sound Lab 10w tube monoblocs at the 2001 Montreal show.