Gateway connected but can not access SSAS tabular, The name provided is not a properly formed accoun

Similar situation. This has to be the simplest configuration possible:

• I have a standalone PC (i.e. not on a corporate network, not in a Windows network or domain) with a lot of horsepower on a fast network
• I have a perfectly functional SQL Server instance for database and Analysis Services Multidimensional
• I have installed the Power BI Gateway, and everything reporting "Online: You are good to go." for the two on-prem databases - the gateway sees them
• If I try to "Get Data" from inside the BI Service, the SSAS data source is listed - the service sees it on the gateway
• But if I try to click on that Data Source Name, here's the infamous, "Something went wrong ... The name provided is not a properly formed account name." error message
• BI Desktop has no problem seeing and building with these data sources
• If I publish from Desktop ("Publishing succeeded") and try to open the result in Service, I get "Couldn't load the model schema associated with this report. Make sure you have a connection to the server, and try again."  

If I read the currently inadequate information on the web for this situation, it sounds like this all boils down to Active Directory.

Seriously? A standalone machine can't push data to the service without being a part of Active Directory? Please, somebody with some credibility tell me that's not the case, and document a REAL solution.