What happen with the power if I add another Pass Aleph 30Theoretically you add 3db. In practise, passive biamping is an expensive way of driving yr spkrs a little bit better. Ideally, to biamp, you need to do it actively, i.e. have the crossover BEFORE the amps. Maybe Tannoy can help you if you're set on this.
I would just stay as is & enjoy the music or, in extremis and if I were using line sources only, I'd eschew the use of the preamp & opt for a transformer volume control.