Interesting. I use Excel pretty often am and good with it but there's nothing compelling enough for me to upgrade from my several-year-old license. The linked .xlsx file isn't readable in the Excel I own.

So you are having a hard time finding qualified people, and you say that using Excel is not an important part of the job description, but you chose to arbitrarily filter out everyone who doesn't own a recent version of Excel.

Does this really ensure only the best and the brightest will apply?

(Spoiler: http://www.zamzar.com/ is an online tool which allows conversion from xlsx to xls; and the 6 questions are not hard, the hardest part is dealing with xlsx.)