Apparently the M9 is not always writing the standard Exif tags for aperture. There are two standard Exif tags and neither are written into the DNG sample file you gave us. I have a sample DNG from another source (ImagingResource.com) that DOES have these tags (both of them). So I don't know if it is because of the firmware version of your M9, or if it is because of the lens you have attached.
I looked at Exiftool and it found a maker note tag "approximate F number" which they showed as 5.0. If you open your photo in ACR, it says f/5.7. So it looks like this 5.0 value is an APEX value which translates to f/5.6 (and rounded to 5.7 from 5.6569 which is the true aperture value).
I will be adding the ability to pick up this "approximate F number" tag in the next build. In the meantime, I suggest you convert your M9 camera DNG files via Adobe's DNG Converter. Set the preferences to create a full resolution preview, and then you will have all the metadata including a full resolution preview not a small preview at 320 pixels wide.
--dennis
