The Supratek Cabernet Dual does exactly what you are describing. I used one for a couple years in my Horn + Sub system for the same reason. There are two volume controls that control different outputs. There are two configurations you can select between via a toggle switch on the back. 1) two separate volume controls one each for different outputs A and B or 2) master slave configuration where one volume controls the gain for output B (slave) and the other volume control controls both A and B keeping the proportion of A & B while raising the volume of both.
Preamp with two volume controls?
Anyone familiar with a preamp that has 2 volume controls. Currently I use 2 Mcintosh C50 preamps in my system. One is for the 2 MC252 amps and 1 used as a volume control for my 3 SVS subs and an Anthem STR amp. The extreme differences in how bass is recorded in new verses old recordings and the wide range in low frequency mastering in the many styles of music I listen to has led me to look for different ways to rectify these issues. What I am doing works pretty well, but I would love to have a more direct method. Thanks in advance.