The problem of finding a suitable serial to USB connector is an old one. The iT person I use explained to me that the variations in the serials are from differences in how they are made. There is not any brand that will work perfect on all computers and it is somewhat trial and error to match one for your laptop to work with the software. I am no computer engineers and found there is a truth to that because my cast off ones have worked for some other techs, they were different brand laptops is the only observable difference however they may have had differences in the operating system also. I literally purchased 3 different cables to find one that would function in the end.
My current version has no USB, only mini C ports. I have not yet tried to run an additional adaptor on a 914 with this on as yet. We may have to hunt for a serial to mini C port next.
Cheers