Hi 

I just tried Chris Rorden's dcm2niiX version v1.0.20170624 with the default options to convert multiband two-shell DTI data. However, I cannot see the bvals/bvecs in the output, just the gz. compressed images. 

I would appreciate if you could tell me how to get these files.

Thank you in advance for your time. 

Best,
Noelia

If anyone has problems converting images, I would suggest seeing if you have the latest stable release, which is available here 
  https://github.com/rordenlab/dcm2niix/releases
there are frequent updates as the vendors update their formats and our ability to interpret these features becomes more sophisticated. I am glad this resolved your issue.