In my opinion this would be impossible to distinguish what was causing the results to look bad...
Lens, Back or decisions in the software.
What can I say ? Of the samples of digital back photos that were made available to me, or those I took myself, only those which were made with an HC lens looked bad to me. If they work for you - great. As to the color of the Hasselblad backs, what I've seen looks OK.
You know how it is - some people like Pepsi, some like Coke, and some admit they can't see the difference