Are you trying to update using the help menu withing the Presonus software or downloading the update using a web browser? What error are you getting? I would try using a browser, follow the instructions here. This will separate the download from the update, please post back here your results.
AFAIK Cox doesn't flag any downloads in any way - they do block certain ports, but none of the blocked ports should be being used during any type of software update. I'd also check your Antivirus program to see if it is being triggered by the update.