Thanks - I tried each step using the default path as well as the full UNC path defined in Deployment\Security Options. When using the full UNC path i got:
Preliminary checks failed! Task Service Error. The network path was not found. (Exception from HRESULT: 0x80070035)
So I reverted back to the default {PackageShare}, which then gave me:
Preliminary checks failed. Task Registering Error. The task has been configured with an unsupported combination of account settings and run time options. (Exception from HRESULT: 0x80041314)
It is worth noting I originally tried this as an 'Installer' with parameters added with and without the quote marks, I have also tried using it as 'Command' with the parameters included in the entire command. The error and HRESULT code are the same for both.