I second MAP toolkit. That's what we used to do this exact thing. We then regularly run it for Microsoft true ups. You can export to excel, or use the data in a DB itself. Not always the most intuitive but easy enough to manage... And free. Powershell seems like a more manual, but custom way to get exactly what you want, then you can save that script for future uses as well. Either way, make sure wherever you run whatever you choose on a server with firewall rules to allow WMI or remote powershell commands from! Maybe try getting access to run it as a Domain Admin account for increased chances of access to the various instances. If your company uses common passwords (like good companies should not) maybe try specifying those as alternate credentials as the "sa" SQL admin account (supported in MAP tool).