Another dumb question

It depends on what the gain value is for each amplifier.

I had a similar experience when I replaced my 2 channel aragon with aragon palladiums, which are monoblocks, with my bk ref 20 in my theater set up... I believe that the preamp section of the processor your using is not strong enough to give the max gain to the amps... yes the power doubled so there should be noticable gain difference.. but if the preamp is not capable of the gain control you would need to "turn it up" higher to get the same volume in db as before... I dont know technically why, but that is my personal experience.
Good Luck!

The input sensitivity of the amplifiers is different. Simply, the Bryston requires more input gain from the preamp to get them to "Go". The volume indicator on your preamp is a very poor measure of how loud your system is going to play, especially when swapping amps around that have different input sensitivities.

The info above regarding the input sensitivity of the power amp constitutes the majority of the answer to your question, but there is one other piece of information that may help you to understand what is going on. There is often a misconception about the "volume control" on the preamp. Volume controls don't actually "turn up" the volume, although that may seem to be the case. Actually, the volume control is an attenuator, which turns down the volume from its maximum output. If you were to remove the "volume control", the preamp would simply operate at maximum voltage output. Hence, the volume control actually decreases the voltage from the preamp's maximum full output.

In many preamps, the volume control is anything but linear. Many volume controls have a rather limited operating range, reaching close to their max output by the time the control knob is around 11:00 - 12:00. If your preamp volume knob must be turned beyond 12:00, it's really not a big deal -- it simply means that the volume control has a more usable "range" before reaching the point of lower attenuation.