You may want to look into a Harlequin RIP. You can demo the HP Z6100 RIP from the following link:
Digital Proofing RIP Software for Epson, HP - Proofer Software for Epson, HP
If you are using three of these printers, you may be able to get by with one RIP computer but I would recommend three separate RIPs with three separate computers. If you need ultimate throughput speed then this is the way to go.
You may want to try the following: Setup the RIP software to output to shared windows printers. To do this you would need to setup a shared Windows printer for each of the HP Z6100 printers. Next, you will need configure the RIP with different setups so that each setup prints out to the appropriate shared Windows printer. This way, the RIP is outputting only a file to the shared printer and your RIP is only tied up for the time it takes to write the file to disk and output the file. You would not have to wait on the printer to start or stop printing before you can send out another job to the other printers.