I read:
i don't think that emulating such a chip is hard but the way to handle the "instruments", the chip is not the most important part as the "power" of its sound has been mainly due to the trackers that were controlling it (ADSR, LFO, "oldskool effects" ...)
http://www.geocities.com/SiliconValley/Lakes/5147/resid/ would be great if someone turned this into an external, how about the stella soundsystem next ?
regards,
x