So it looks like there is no SID socket here? The 2 that I thought were SIDs are actually OPL2 , a VERY NICE SOUND CHIP, I might add, but not a SID. I'm assuming that the FPGA SID HAS SUFFICIENT CAPACITORS to emulate ANALOG synthesis?
If I remember well anyway the SID hardware is digital and its only the last part how is converted in analog waves (really bad one on the scop you need a low pass filter to get analog waves instead of weird PWM). Some version on Yamaha synthesizer keyboard (if not all) didn't event had the digital to analog converter built in, they had to add a separated chip to do the conversion. So as long as you get the ADC matching the SID one (I guess) you will have the same sound from en FPGA
If I remember well anyway the SID hardware is digital and its only the last part how is converted in analog waves (really bad one on the scop you need a low pass filter to get analog waves instead of weird PWM). Some version on Yamaha synthesizer keyboard (if not all) didn't event had the digital to analog converter built in, they had to add a separated chip to do the conversion. So as long as you get the ADC matching the SID one (I guess) you will have the same sound from en FPGA