Thanks for your response, Chris.
Unfortunately, I really can't see where your response is accurate. I don't think this extension has anything to do with importing data INTO QuickBooks. The description of the extension on AppSource is as follows:
"Import payroll transaction to Dynamics 365 for Financials from files in the Quickbooks IIF format. Aggregated payroll data, including date, payroll account, description, and amount, will be imported to your G/L accounts according to mappings that you perform once per payroll account".
This description basically indicates that I'll be using the extension to import data INTO Financials. I don't see where it would make any sense to be exporting data OUT of Financials and into QuickBooks. This is especially true for salaried employees.
Once you install the extension, you'll see an additional action on the General Journal screen. When you click on this action (i.e. "Import Payroll Transactions"), you are prompted with the following message:

When I select QuickBooks, I get the next screen:

I then go through a series of dialogs to import the P/R information INTO Financials. The Ceridian import works pretty much the same way. In each instance, either QB or Ceridian is used to process payroll, with the result being imported INTO Financials as a G/L entry.