Zanash pretty much hits it on the head - 6w will provide a surprising amount of volume from most modern speakers, but it's still only 6w.  I'm running an 8w push-pull amp into 89dB/4ohm(3.5ohm min) Audiophysic Avanti IIIs and 8w seems to be plenty - it is surprising how most of regular listening is in the first couple of watts.  Certainly in my room (18'x16'x10' or thereabouts) I can get more than sufficient volumes (i.e. beyond comfortable levels) with my amp:speaker combo.