color - Simplest set of inks that could print the RGB gamut?

Artist Tauba Auberbach produced this recently:

It's called RGB Colourspace Atlas, and is a physical, printed book of what it implies is the whole RGB colour space.

Is there an existing commercially available ink set that could print something like this? Naturally, CMYK printers couldn't do it because they don't cover the full RGB gamut - they couldn't reach the pure reds, greens and blues. And for spot colours, mixing and blending them is a Bad Idea - not what they're normally designed for - so it's hard to see how they could be used in the complex hue gradients.

Could a hexachrome (CMYKOG, Cyan/Magenta/Yellow/Black/Orange/Green) ink set manage this? Or CMYKRB (.../Red/Blue)? Or anything else?

(Bonus points if anyone somehow knows how this exact book was printed, and hat tip to blog Flowing Data)

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Edit: just saw these after DA01 and Brenden's answers, which suggests that Hexachrome gets close to the sRGB gamut but doesn't reach all the blues and doesn't quite reach all the greens:

Source

...and this which suggests HP Indichrome 6-colour doesn't reach all the reds and blues, and quite a lot on the greens (so you'd expect Indichrome Plus to get close to, but not quite reach, the RGB greens):

Source

Answer

The site doesn't say which RGB gamut, so the question has a bit of a hole in it.

HP doesn't give any specs and makes no claims that I know of (I just checked again on a couple of their spec sheets) in relation to reproducing an sRGB or Adobe RGB gamut. They do, justifiably, guarantee accurate reproduction of most of the Pantone colors even without using their offline ink mixer. They do offer Photo Cyan and Photo Magenta, essential for photographic reproduction (which speaks to the RGB color space, of course).

I'll be visiting one of the best digital printing plants in the world a couple of weeks from now and will check. All their digital work is on Indigo, and HP uses them to showcase what the presses can do, to potential buyers. If anybody knows, they will.

The only printer I know of that claims to reproduce the Adobe 1998 RGB gamut in full is the Canon Pro9000 (not the 9500, which uses pigment inks). That requires the right ICC profile and the right paper. I've not tested that claim scientifically, but I can say that it has the best color gamut of any photo inkjet I've used and is a dead-on accurate proofer for CMYK print or grande format work. The Pro9000 uses C, M, Y, K, Photo Cyan, Photo Magenta, Red and Green inks.