You could check out the link below and then call Steve or Patrick at SMc.
Even with the upgrades, there are considerations related to the age of the DAC such as whether to switch to an R2R ladder type DAC, or other different technologies that are now available. However, from the standpoint of power supply and parts improvements, I suspect SMc upgrades would make the DAC sound as good as it possibly can using the technology it is based on.
http://www.6moons.com/audioreviews/smcaudio2/dac.html
Even with the upgrades, there are considerations related to the age of the DAC such as whether to switch to an R2R ladder type DAC, or other different technologies that are now available. However, from the standpoint of power supply and parts improvements, I suspect SMc upgrades would make the DAC sound as good as it possibly can using the technology it is based on.
http://www.6moons.com/audioreviews/smcaudio2/dac.html