Like an awful lot (most?) PR blurb, the expression 'grandeur nature' doesn't actually mean anything in particular in this source text.

And like most PR blurb, it needs rewriting in the source language, trying to get across a similar overall meaning, rather than merely translating the words.

I can only think this refers to the size of the screens, up to 56’’ (142cm). Of course when you have a screen of any size, some things can be "lifesize": anything smaller than about 30cmx30cm can be displayed "lifesize" on my computer screen, but I'd have trouble getting a lifesize view of Tower Bridge, Sebastian Chabal, or even Claudia Schiffer. And not even the large Philips screen can do that (otherwise I might get one).

I agree with Mediamatrix that it's not a literal use of the term, but just PR blurb, which you could translate with "breathtaking" or any other adjective you fancy that gets across the "wow, isn't it fab!" idea (sensational, thrilling, etc. etc.)

It means "in real conditions" which is rather clumsy here, so I suggest "to experience the multimedia functions first-hand" or something along those lines.

Cf. Web.Ref.