Thank you, Kevin!
If I had extra time, I think I would look into this issue in more detail as you suggested. However, as a PhD student I've got a mountain of research to do and deadlines to meet, so I will just stick to using USB-6341 as for now it does everything I need. Hopefully, MathWorks manages to improve Data Acquisition Toolbox and sort out the way how NI cards interact with MatLab!
