If you want install one of these, do you need to remove the cross memebers/under brace?

And they bolt right up to where the cat normally sits no problem?

then question about the sound, videos seem like it rasps a bit between 3&4k but other wise do they make a good difference with the sound with a stock cat back?

My main sound concerns are drone, lots of rasp, and being way to loud.

 

Yes

Yes

Yes, there is rasp inbetween 3k and 4k. The obnoxiousness of the rasp is dependent on the amount of throttle pressure as well as the catback you pair it up with. Here's a video of the midpipe paired up to the stock catback:

http://www.youtube.com/watch?v=PvE9DeG3YP8

To answer your final questions, the midpipe does not really "drone", but it pops and pops and SHOOTS FLAMES. You're going to get rasp inbetween 3k and 4k; some people love it and others think it's annoying, but rasp exists in most midpipes with our car and the only way to get rid of it is by paying $400 for a BHR midpipe. It is notorious for being one of the louder midpipes, but again, it all depends on the catback you run it with. I don't think it will be too loud paired up with the stock exhaust.

 

I removed the under-brace by the catback, but I don't think you really have to. They bolt up no problem, but you will have to get 3 new bolts/nuts to mount to the header down pipe.

As for the sound with a stock exhaust I can't say as as I installed the HKS Hi-power at the same time and that set up is defiantly raspy and loud.