Personally I dumped recabinet 3 in favour of amplitube free, and spending a few quid on some cabinets. I turn off every part except the speakers and mic section so its just used as a cab sim not an amp sim.
It has a very nice (well I think) room mic set up, and the ability to mute the cab mic so you just get the ambience.
So you could run your preamp signal in to recabinet to get the sound you like, and a copy of the preamp signal into a similar cab in amplitube and just use the room ambience mics. Then layer the two together. it comes with some decent free cabs to start with and if you're just after ambience then one of them will probably do so you wont need to spend any cash on it.
Or just amplitube for it all
but that's all a matter of taste and suggesting one sim is better than another is a pointless debate. But the ambience of it is very nice.