Well, the thing about the SID in particular, is that it relied upon imperfections in the MOS silicon fabrication process to produce certain analogue effects (a fairly common approachh in electronic instruments in the 80s). Problem is, that as processes improved it gets harder to produce noise in this way. The later generations of SID produced a “cleaner” sound, but not faithful to the original to the point that certain effects exploting these imperfections (eg some funky sound sample techniques) were broken on the newer version. I’ve read somewhere that it isn't possible to produce the SID at all with modern technology because processes are just so “clean” now.
