Do you have your IRD set to block the SD duplicates of HD channels?
Go into your unit's setup (at least for the HR2x series) and choose to not hide the SD duplicates. The SNY 624 SD version should be visible after making this change.
Go into your unit's setup (at least for the HR2x series) and choose to not hide the SD duplicates. The SNY 624 SD version should be visible after making this change.