If you are using your Octopre with a step-down/up transformer and are experiencing sync problems then it could be down to the quality or age of the step down transformer. If the converter is getting slightly less power than it requires then loss of sync may occur - it may be that the
transformer is older and expecting a slightly higher supply voltage than is present. There are other things which could be causing loss of sync but if your transformer is old or poor quality then it may be worth trying a different one to narrow down the cause of the problem.
Note that the fact that a step down transformer may cause jitter in the mains signal will have no effect on the converter jitter since the crystal used always has a jitter figure of +/-10psec. Therefore using a good transformer with the Octopre will not cause any problems when using the digital card.