Hey there,
You have a bug in your Copy-SqlAudit function. It reports "Cannot bind argument to parameter 'Path' because it is an empty string." when you are trying to copy an Audit that writes to the application log. It's the check on the file path that's failing so I wrote a fix for it if you're interested.

My new line is simply:
if (($audit.Filepath) -ne $null -AND $(Test-SqlPath -SqlServer $destserver -Path $audit.Filepath) -eq $false)

That's all the old variables so would need to be updated to using test-dbasqlpath -sqlilnstance