Another dumb question

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.

Slartibartfast has the right point. Very often high powered amps require higher input voltage and so you should match the preamp for your new amp.

No dumb questions ;just dumb answers. Sounds like a gain situation as descrbed above; good answers.

I think in many cases the input sensitivity of the amp needs to be almost 100 times that of the output sensitivity of the preamp for a good match. This varies however depending on the particular components and/or manufacturers being matched up. I've run into this same problem but only when trying to integrate a powered subwoofer. Good luck.