Richard,
Have you verified that the 3D Transform is not changing the color by introducing shading? (See my reply in your other thread):
<http://www.adobeforums.com/cgi-bin/webx/.3bc0d56d/1>
The printing process will always by necessity bring the color into the printer's native gamut. So even though the application's UI may display numbers for a specific RGB color, that doesn't mean that's what's really being printed. RGB is not an absolute color specification (like Lab is), it's a percentage of power on a 3 diode light device.
Many modern inkjet printers, though, have six or eight inks, and have gamuts that are wider than the traditional CMYK gamut. The new Pixma Pro 9500 (released last February) has ten inks! Every year somebody seems to come out with a newer printer with a wider gamut than last year's. This is one area where software has not quite kept up with the printing technology. You can't work in RGB or Lab and ask to get out-of-gamut warnings only when it exceeds the gamut of your specific printer, where the printer is not a CMYK printer. I wish you could, since I use one of those eight-ink printers.
I have found, though, that the printers do not take as much advantage of their extra inks to increase the gamut as one might think. They do have wider gamuts than traditional CMYK, just not as wide as they would be if increasing the gamut were the top priority. They put more emphasis on getting denser smoother ink coverage and avoiding visible halftone patterns. (The Pixma's two extra inks beyond the 8 that are in my Canon i9900 are two additional colors of gray, to give exceptionally smooth monochrome prints, not something like hot purple, neon orange or cobalt blue that would significantly increase coverage of the RGB gamut.)
Still, I would not be at all surprised to see a printer with twelve inks and a nearly neon-like range in two or three more years. It would be nice if the print driver could broadcast information about its current range (in case it has dynamic settings as to which inks you want to use), and the design software could use that to inform the out-of-gamut warnings.