Hi fab,
an alternate solution (if the HP switch supports it) could be to use a QSFP -> 4 x SFP+ optical breakout cable. This cable gives you 4 x LC connectors which you can patch to other equipment. These LC-connectors can the be patched to to ordinary SFP+ SR optics in the SRX550.
If you move on with testing the QSFP -> 4 x SFP+ DAC cable, please remember to use a cable below 5 meters as I would guess there is a chance that a passive cable will work, but active cable (>5 meters) won't.
