I have both. As Bob mentioned, the PLC is electrically noisy and must be located carefully away from your signal path. The SDS doesn't have this problem. The PLC is a more primitive design with analog control knobs, while the SDS has push buttons and a digital read out. Having said all this, I haven't heard a big difference in sound quality, although the SDS has been praised by the magazine reviewers (better ears than mine, I guess). Good luck.
