Well, okay, if I were living in a alternate universe and actually owned speakers that are 83.5dB/2.83v/m, instead of 93.0dB/2.83v/m, I would most likely use an external amp too.
But just looking at this 83.5dB/4 ohms speaker, even if the OP had a 300 WPC amp, which is probably 450W/ 4ohms, with the same parameters, this would only output a peak SPL of 103dB, which isn't that much more than what the Denon 3805 could do at 101dB.