[Bret Bolton] "Is it possible that the .dpx sequence is also a "wrapper" or a series of REF file(s) pointing to the original Quicktime movie (which I do not have)?"
no.
the "wrapper" is so the Quicktime can read the files on the mac, since mac's do not read the frames directly.
are you working on a Mac or a PC"?
how are you importing the files into WHICH APP?
have you looked at the DPX files in something else ( photoshop) to see if they open.
you have operator error either in how you are importing the files or who produced them for you
gary adcock
Studio37
HD & Film Consultation
Post and Production Workflows
Inside look at the IoHD