I'm actually surprised that not all amp simulation coding happens with reference tracks right there the whole time.
You need to have the resources. I have been fortunate enough to find someone willing to do the reamp for me this time. You know, I don't own a Recto. I have an XTC sim almost ready to be released and I have not been able to find someone to do some reamping.
I do my best to make my sims as much accurate as I can but... I don't have all the resources. That is probably the same for most (if not all) of the other freeware developers.