Check this out..Speaker Sytem Modeler for Mixdown testing...

[XLR8A]

The best solution for mastering is to use couple of different pairs of monitors
and different rooms, one room accoustically threated and the other one
completely naked. Near-field monitors, mid-field monitors and stay-away-field
monitors (pa speakers). Btw, Sony studios have a special room with a real
car inside, that equipped with a decent car stereo system - that's some
original and very good idea for mastering purposes.

Ofcourse most important is always to keep a pair of good and fresh ears.

[Gopal]

I really don't see the difference between this product and a convolution reverb. They are both designed to give the impression of hearing a song in a particular space or give the impression of hearing through a particular type of speaker. It won't sound the same of course but it will 'give the impression' to at least let you know whether your track would rock a big room for example or just sound thin. That's what I make of it anyway