PCs printing "different" colours than Macs

Question

I've got a potential client with a problem and I need to better understand the basic processes before I go speak with them. They have 3 designers in-house and 1 salesperson, all of whom have Adobe CS installed. Two designers are using Mac, while one designer & one sales person are each using PC. All four print to the same desktop inkjet printer.

When either of the Mac users sends a .PSD file to the printer, they get "different" colours than when their PC using colleagues send the same files to this printer.

What are the mostly culprits for such a discrepancy? I assume the conversion from RGB -> CMYK must be differing between the OS'es, but before I go in to have a look I need to know where these conversions are typically done: Creative Suite? the OS? the printer itself?

I'm assuming I can rule the physical printer out since it is the one constant - though perhaps there is a driver-level issue in the OS'es. The users are all aware that colours on screen may appear differently than printed colour, so this seems to be a PC vs Mac issue from what I can tell. The basic complaint is that:

"The PCs are printing the documents differently than the Macs."

Answer 1

There is a severe bug when it comes to printing on a Mac in Photoshop CC 2015.5 that Adobe acknowledged at last a few weeks ago. Maybe your clients are affected by this problem.

See this page by Adobe about the problem.

And here is an in-depth description of the issue. That should help you identify, if your clients have this specific issue.