Thanks for this. DSPs that accurately simulate hardware are not as trivial as one might initially think. I've done some thinking on this front, and the DSP based approaches that simulate hardware are likely making many shortcuts. Take a zener limiter circuit for example. You could just rail samples with an amplitude comparison, but that's a bad sound. So what I think most limiter DSPs do is apply a shaping filter to that. It's an approximation, but not really capturing the characterization of the circuit. The simplest way to get an accurate response is with SPICE simulation. I'd love to see a DSP that specialized in realtime SPICE simulation. Failing that, you have to sit down and do the math for each circuit yourself to establish the relationships between component values and signals, then code that into your DSP. It's not an unreasonably large amount of work, but judging from the people I think are selling audio software, I would be shocked if anyone is actually doing that.