Pasive Amplification or Monoblocks ????

I think you'd be surprised at the amount of definition you would achieve if you passively biamped your speakers. In my experiences the improvements go way beyond adding 3db. Your Tannoys need to be biwireable, that is separate taps for low and high frequencies at the speaker. To biamp you will need another pair of matching interconnects and speaker cables to make all the connections. You can find another pair of Aleph 30s on Audiogon.
It made all the difference in the world on my Revel Salons and Magnepan setups.

What happen with the power if I add another Pass Aleph 30

Theoretically 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.

Stay where you are, you are heading problems IMO. If you want a change I would try an X250.5 or an XA60 in the future.

Fernando