Look into impulse responses on past threads here on GC, or google elsewhere. It's a good way to get realistic cab simulations and ambient reverbs. You'll need the impulse files, and a convoluter (or was it convolver) plug-in to read them and apply to your tracks.
What they are actually, feel free to correct me, are recordings or snapshots of the transient response of an actual enclosed space and how the instantaneous reflection travels. These impulses are then fed into your recordings, which should give you a close representation of sound as if you miked the cab yourself, or stood inside a recording space with your room mic.
