cmf

Me personally..... I think the IS was slower than the TSX for one. Maybe it was the way it was geared being a 5-spd, not really sure. I haven't compared numbers, but I know that others have discussed it before.
Fit and finish..... The gauges are a bit played out with the watch looking instrument cluster, and a lot of things we get stock end up being options on the IS.
Stereo/ sound system is one in the same to me, both equally good. Cabin noise, I'd say the IS might have a small edge being a bit quieter. Seating is virtually the same, in regards to legroom.
Both cars being parked side by side, same price tag, same options, nothing different of the two cars aside from styling, I'd still take the TSX. The IS has a good platform to build on in regards to performance, but I believe looks go a long ways, and the TSX looks way better.
The TSX is cheaper too, so I would say..... TSX!

The IS is not a bad car, but not worth 30K +.

Not too sure you were looking for more info than that.