No one comes closer to offering this functionality than Parasound, to my knowledge.
But a few observations…you start by specifying all analog, like a purist passive preamp, then throw in active circuitry, which means op amps, then a full electronic crossover with every option, and where do we arrive in the end? At DSP, the only practical way to do all this. And there are DSP units from as diverse sources as Dayton Audio to miniDSP to Lyngdorff.
Somebody Please Make This Already...
Imagine an interesting new product: Two sets of analog inputs (when I say sets, I mean each set has single-ended and also balanced), one volume attenuator that controls output synchronously BY WAY OF TWO SETS OF SYNCHRONIZED RESISTOR LADDERS (analog-domain attenuation, not digital) between the two sets of inputs, and then matched sets of outputs (again, both, single-ended and balanced). The entire device should be active, so that if you use single-ended input, it can still output a balanced, differential signal after the volume control, and on the output end there should be an option to combine L/R signals into a single signal (like an LFE output).
Even better yet, we should allow adjustable high-pass filter on the first set of in/outputs and an adjustable low-pass filter on the second set of in/outputs. Slope and frequency should both be adjustable. And of course both filters can be separately bypassed.
The unit should also have a single 12V trigger input and three 12V trigger outputs, and it should have a remote control that can control volume, filter slopes and filter frequencies.
-Ed