Let me preface this with I am a Software Engineer who dabbled in created an amp modelling plugin, and I read a lot of research papers on amp modelling techniques. I spend a lot of my time explaining why it's so difficult to change the color of a button.
If you can model a tubescreamer, which is one of the examples that pops up a lot as a simple thing to model, you can model solid state.
The State of the Art component modeling technique is to run a simulation of every component on the circuit e.g. SPICE.
From what I understand, none of the major players model the entire circuit at once, they break it up. For example pre amp, tone stack, power amp, etc. This way they can reuse the same modeling code, but change the component values to match the amp. (Which is were I gave up because I don't have an actual amp or the tools or expertise to measure one).
My educated guess to OPs problem: The developer didn't plan for multiple preamps so they are limited to 1 preamp with different parameters for each amp. Changing that would mean refactoring the whole codebase which is a no go for a small company.
Coding is the easy part of software engineer.