Moral: Use genuine Xerox cartridges (a set possibly costing more than the printer) or take your printer's life in your hands!
LATER UPDATE: MORE DETAILS
Now to my best (but imperfect) knowledge, the mechanism is this. Xerox printers (the 6000 and for all I know all) have a "mantrap" against use of incompatible cartridges. Xerox define "regions" of the world (e.g. Europe). The (low capacity) starter cartridges that come with the machine have no chips and so are universal (no region). The machine similarly starts out universal. The first time you put a normal, chipped cartridge in, the machine sets itself to the region in that cartridge's chip. It will then accept no chipped cartridge from any other region. Also, once you have tried a chipped cartridge, starter ones are rejected in that slot.
I was unlucky enough to buy a "compatible" cartridge on Amazon that seems to have been of a non-Europe region. It will now reject any proper cartridges, even genuine Xerox. I have had to buy another machine (and will then pay what seems to me to be the very heavy price for genuine Xerox cartridges.)
Xerox sent out service engineers out under warranty. They were understanding and helpful. They said that Xerox have a small program that sets the machine back to square one and that they would arrange to send me a copy. I am still waiting after a week. I have a horrible suspicion (no more) that the managers and engineers do not want this "key to the mantrap" to get out into the world, and have ordered the people I dealt with to clam up.
A MORAL might be: Look at the prices of genuine Xerox cartridges, and do not buy this machine unless you are prepared to buy these, or risk your machine's life.
To be fair, this seems so far to be a great printer, easy to install and does all that I want of it - basic text printing with a colour option. Research had told me that all laser printers produce rather "soft" colour images. In fact, on very standard paper, it produces photos that, if not quite up to an ink-jet on photo paper are surprisingly good and quite glossy looking. Even in draft mode (a box for this is somewhat hidden in the Advanced page of the Settings window) both colour and b/w prints are very usable.
An interesting power-saving feature is that the printer seems to have the capability of turning its mains power switch off if left unused for a (programmable) time!
HOWEVER, for several days of use it gave regular paper jams - roughly every other print. A sheet of paper was left at the back of the machine, as if it had picked up a second sheet and fed it through immediately after the first. A little fiddly to remove, not difficult once I had learned to be careful not to tear it. I tried three weights of paper, all good quality and condition, fanned before insertion. Before reporting this to Amazon and asking for a replacement, I tried to get support from Xerox. Total failure! Websites listed in the manual did not seem to exist, and one I got to via on-line search sent an auto acknowledgement promising 48 hour response - 2 weeks ago - still nothing. It may still be early days, but the jam problem seems to have resolved itself, so I shall not have to bother Amazon (who I am sure would respond efficiently as usual). I also cannot claim to have exhausted the options for trying to contact Xerox, but the initial impression is not good.
LATER: It is a bit early to be 100% sure, but I think I now understand the jams. Our previous (HP Deskjet) printer handled some pre-existing documents perfectly depite the fact that the paper size set in Page Setup did not match the actual paper loaded. The Xerox software seems much less well written, and throws paper jams in this situation. (For the record: historic Microsoft Office applications and Windows XP.)
You may find buying new cartridges a little confusing! This printer is sold as P6000V_B. Its software calls it P6000B. Cartridges on the market seem only to be for P6000. I have struggled to find any of these on Xerox website, and am forming the impression that they are great at making printers, rubish at helpful documentation! I just hope that all these numbers refer to the same device.
I am now fairly sure that the cartriges that come with the printer are "starter" ones, with not much toner in them. Since it would be cheaper to buy a new printer than a set of full price Xerox cartridges, perhaps this is no surprise! (Compatibles are cheaper - ~half the printer's cost for a full set. Suggest you factor toner costs into your buying decision.
This printer is a great printer! The quality is superb! I have had several different kinds of laser printers, but Xerox Phaser 6000 tops them all! My main purpose is weatherproof decals. When it prints, it prints with amazing results. For instance, when I would print with Reds with previous printers, they would have a pinkish cast. Not Xerox Phaser! It is totally perfect. I am very happy with this printer. There is only on flaw though, if you are printing in multi pages (1-10 etc) it has a tendency to jam. One sheet at a time works great though.