I would rather go for Caldera it's much faster then Onyx.
It runs on top of Linux that is free.
We use Caldera for our ValueJet machines (3 printers) and we run them from one PC.
Also we have Onyx Thrieve which is bundeled with our Oce Arizona machines (2 printers) and I must say that it's very slow.
We use Intel i7 3,4Ghz CPU, 16GB RAM, 256GB latest Samsung SSD drive and it's slow...
On similiar setup Caldera flyes.