anon90267- It may depend on how old your DVR is. It was explained to me that when optical cables are used, some older equipment is not capable of handling the power. The equipment may be your issue, or perhaps there is a cable best recommended for that DVR model. Either way a call to the manufacturer may be helpful.
Our internet company is putting in optical lines and informed me that the modem I just purchased from them will not be able to handle the power coming through; they will need to replace it for me.