Depending on your music preference, listening level, and size of room, I would think that 11 watts would be fine.
I drive my vintage Cornwalls with 3.5 watts of 2A3 power and never run out of steam, however my room is fairly small
and I don't listen at very loud levels.
$80 is a steal for these speakers, with the going price usually around $400, I know, I've been looking for a pair to give
to my son. Plan on upgrading the caps in the crossover for a nice increase in sound quality.
Lots of info on these speakers on the Klipsch forum.