Another dumb question

I was pleased with the improvement in quality I had noticed after adding a Bryston 4bst to my mains previously driven by the Yamaha DSP-a1's internal amps. The only drawback is that 4b seemed to require a higher volume setting on the Pre for the same spl as the DSP-a1.Then I borrowed a friends 4bst and bridged them for 800 watts per channel and the volume was less yet! This doesn't make sense. 800 vs 300 vs 110 watts? Hookups are rca and unbalanced was selected at amps. into Definitive tech bp10s. any help appreciated.