Hi Tia, and welcome to the forum.
Unfortunately you've encountered a bit of a Catch-22 situation there: Monarch will only allow you to simultaneously open multiple files using the Open Database approach if the input files are delimited text. Ironic, huh?
I'd be tempted to write a VBS script to handle your task. Which Excel file type are you using: .xls or .xlsx, or something else?
There may similar examples of such a script in this forum. I'll see what I can find. Odds are though that it would be faster to just start coding.
After some experimentation, I finally got the syntax right for a little batch file to accomplish this challenge.
First, you need both a model and a project file to handle one of the Excel files.
for %%i in (*.xls) do Call :DoMonarch "%%i"
("C:\Program Files\Monarch\Program\Monarch.exe" /prj:"C:\test\project.xprj" /datasource:"%1" /exp:"%1".csv)
Copy this to Notepad, revising the drive letter and folder names and the project name as necessary and save it as "XLStoCSV.bat".
The end result of running the batch file, as shown above, is that all of the .xls files in C:\test will be converted to .csv files.
If the folder contained three files named Export1.xls Export2.xls and Export3.xls then the folder will contain Export1.xls.csv Export2.xls.csv and Export3.xls.csv
Windows won't care about the .xls in the middle of the .csv file names.