sanderx: just a minor correction. The m³ with opa604@40v will give roughly 22Vp-p (7.77Vrms). So you won't even go above the max power handling.
Uncle Eric is right in saying that people who want to go to tubes should go to tubes. With the caevat that they shouldn't go to tubes because solid state / opamp based amplifiers supposedly don't have enough voltage swing.