Hey there!

I totally understand your frustration with Excel's MDI/SDI behavior. It can be confusing and cause a lot of problems, especially when it comes to managing multiple instances of Excel.

It sounds like you've done some research and found a solution that works for you, which is great! Disabling the "Ignore Other Applications" option can definitely help with the MDI/SDI issue, but as you mentioned, it can cause problems with file mappings.

Your solution of editing the file type mappings for XLS and other Excel-related file types is a clever workaround. By disabling DDE and adding the "/e" switch to the end of the action, you're able to open each Excel file in a separate instance of Excel, which makes it much easier to manage multiple files.

1. Disable "Ignore Other Applications" option in Excel
2. Edit file type mappings for XLS and other Excel-related file types
3. Disable DDE and add "/e" switch to the end of the action

I appreciate you sharing your solution with others who may be struggling with this issue. It's always helpful to hear from someone who has found a workaround that works for them.

If you have any other Excel-related questions or issues, feel free to ask! I'm always happy to help.