Shooting in DX mode won't help one bit. All you're doing is cropping the photo. Your best bet for now is to not use the converter and increase your ISO to bring up the shutter speed. Posting one of the soft photos with the EXIF data intact would help us see where the problem is.
Nikonians®, NikoScope® and NikoniansAcademy™ are trademarks owned by Nikonians.org.
Nikon®, Nikonos® and Nikkor® are registered trademarks of Nikon Corporation.