Thanks a lot for your answers, I have tried both vertical bi amp and bridged mode. The differences are big. The DR9 used in stereo has the sound of valves amps. When bridged you gain bass ,definition and more space (mainly depth).
I finally stayed with bridged mode as I have found it's the best for my configuration, the definition is impressive.
I listen classical music at around 80 db so I don't think it may be a problem.
