I have IPL s3 speakers that I use in a room only a little larger than yours, powered by a Monarchy Audio sm 70 (which is 20 watts or so class A transistor). I have no problems with lack of power, but I dont need head banging levels..in fact I am giving serious thought to getting a SE valve amp kit.

I love my IPL speakers they have great bass, clear open mids and glorious ribbon tweeter. They are  around 89db sensitivity, with a smooth easy impedence curve.

I see that IPL now do a higher efficiency kit but I havent heard that, or an Oto SE, so I can't give you a full answer.