Interesting file conversion issue. One solution that claims to work cost $30.
.xls to .dts at this site, asking for $30 for the software: https://www.winsite.com/convert/convert+xls+dts/index3.html
there might be some xml to .xxx conversion options but you will have to search. There is always working on writing a program to format the data. Maybe the $30 shareware is a better option??? I once used a software called Sigma Scan Pro that did some awesome image file batch format conversion. I am not sure if it also does data file conversion but I recall it having an excel like interface. The last time I used was 2000. It's for data analysis. Just a thought that came to mind. Good luck.
You can try to convert Excel file to CSV (comma delimited) or use another software to deconvolute your XPS spectra, XPSPEAK 4.1 is a free option or Origin Pro suite that you can use .XLS files directly.
What do you want to do? Put a 2 column file into the apparatus software to process the spectra? Problem: the instrument software usually needs all the headings in the original file to "know" the measurement conditions (i.e. energy ranges, step size, etc) to be able to process it, lets say background subtraction, peak identification and so on. If your excel file is only 2-column with data and no headers, then I suggest you to try processing manually as Rafael Tolentino suggested, as the instrument software will probably do not recognize the 2-column file even if it could be converted to xps-like data.