Hasselblad has not offered any guarantee that the H4X/H5X will work well with the Phase One IQ or P+ digital backs, and it is therefore difficult for Phase One to recommend this as a viable solution.
We have already made several discoveries regarding compatibility concerns between the H4X/H5X and Phase One IQ/P/P+ backs but due to Hasselblad’s closed system these errors are difficult to diagnose completely.
Some of the issues have already been addressed in IQ firmware version 2.0 and above Which is available here http://www.phaseone.com/en/Downloads/Firmware/IQ- Firmware.aspx
And by Hasselblad with firmware 2.2.5 / 16.0.6, contact your source of purchase for firmware update.
How well will the H4X/H5X work with an IQ or P/P+ digital back?
H4X/H5X and IQ digital backs: There is no know issue after release of firmware 2.0 however compatibility still can not be guaranteed due to mismatch between the H4x's protocol vs. H1/H2.
H4X/H5X used with P and P+ digital back may suffer from problems with communication and a capture speed decrease of approx. 20%. It is recommended that if you must use an H4X with a P+ back, you use the latest firmware.
Unfortunately Hasselblad has not informed us about the H4X/H5X prior to release nor does the H4X completly comply with the H1 and H2's way of communicating.
There also does not seem to have been any type of compatibility test from Hasselblad.
Based on these concerns it is difficult for Phase One to recommend users to upgrade to H4X/H5X.