How to check the manufacturer's preferences RGB versus CMYK:
Download the program ICC Profile Inspector:
http://www.color.org/ICCProfileInspector2_4.zip
Open one of a couple of available ICC-Profiles for the printer.
Check by Profile Inspector whether it is an RGB–Lab profile or a CMYK–Lab profile.
If these profiles are RGB-profiles, then the manufacturer considers the printer
normally as an RGB device.
But stop!
I'm using since many years
1. large format inkjet printers Mutoh 6100 and Epson 7890,
operated by RIP Colorgate Productionserver, earlier by RIPs Onyx and Best-Efi.
2. toner printers OKI 9600,
PostScript devices, operated by Photoshop and Acrobat.
For the calibration I'm using in all cases large or small CMYK targets, printed without
color management by Photoshop (older version, which has this mode) for the toner
printer and by RIP for the inkjets. Profiles by GretagMacbeth ProfileMaker.
The manufacturer's profiles for the Epson are RGB-profiles! All my profiles are
of course CMYK profiles. The inkjets are often used for proof printing for offset.
A remark to post #4: it seems that the mentioned test was done without any profile.
Then it is of no relevance.
Best regards --Gernot Hoffmann