"Although I was unable to make the 600 drivers work with the 550C, in the process I "inadvertently" updated the HP Background and HP PrintMonitor files to versions 4.0.7 and 3.0.8, respectively. Saving these files and deleting the others (i.e., DW600 driver and HP CMM2) eliminated the crashes! I've been in contact with HP Tech Service, who have not discouraged the use of these updated files with the 500-series printers."
Update: Jason Licht reports that this fix does not work. He has heard that the problems are due to a virtual memory conflict; printing with VM off works.