A movement from an SDS to an ADS is not an "upgrade." They both are designed to do about the same thing and with the same level of quality. Unfortunately the ADS has been found by many users to be noisy, that is, to produce a vibration that can be heard if it is near the listening position. Best guess offered over on the VPI site is that VPI has used a very cheap transformer inside that simply vibrates. Seems that it needed, but did not get, a redesign upon its launch. That’s why many people are looking for SDSs and the used price is holding up.
Too bad no one has picked up on the Falcon/Eagle/Roadrunner designs.