Hi Sarraval
I was testing lighting in large rooms last week, i found that splitting the room into 4,ie, 4 individual rooms, and then using the newest version of EnkoNyito's plugin, the results were not too bad, also using 2 large invisible light panel's like here, also gave a reasonable result.
But whatever solution you find it will undoubtedly involve additional light sources, path settings or enhanced external brightness.
Mike