I have the 1.8 mkII's and I do not think that they need a lot of volume to shine. I get very smooth midrange (the reason I bought them - female vocals) at low levels. They tend to be somewhat bass shy until you put the juice to them. However, the more power you put to them the better. I am using a 100w Adcom power amp and will soon be upgrading. By the by, I think to Contour center (not the new 2.5 center model) is the most natural speaker I have heard for what a center channel is supposed to do, reproduce people speaking.
At the dealer, I thought that the 1.3's needed more volume to shine, that was why I went with the 1.8's( I wanted the 3.3's but my wife balked)