This is exactly what Fractal has achieved. They took actual amps and modeled the actual circuits. Basically, this work was done for a massive number of amps by

This is exactly what Fractal has achieved. They took actual amps and modeled the actual circuits. Basically, this work was done for a massive number of amps by one dude. And he sells this device for $2k - which is ~ the cost of a single good tube amp head.