Well, the Rega Brio-R doesn't have HT-bypass so I can't use preamps from an av-amp I am afraid.
You can (I do); it's just a little bit more faff.
When you use for AV, the signal goes through both preamps. The volume is put to a set position on the Rega, and the AV amp is then calibrated as normal. Then when using for AV, just return the volume of the Rega to this set position, and control from the AV amp as usual.
Two channel works as normal with the AV amp off. The only downside is YOU MUST REMEMBER TO PUT THE VOLUME BACK on the Rega when switching from AV to stereo.
The slight degradation from going through 2 preamps is only for L&R (25% of the sound), so isn't a big issue. Just try to get an AV amp (with preouts) that sounds as close as possible to the Rega.