Markus - if you're interested in a deep sounding muffler try the "other" 5zigen mufflers. I myself don't like the fireball sound much. On my other car I have a 5zigen border dual tip rearsection. VERY VERY NICE SOUND. Deep, bassy sound...I like it a lot. I wanted to get a similar setup for my Sube...but ended up with a great deal on my Blitz so~
As for Tenzo and Ractive..well..they're ok. If you want to put it on your car its ok. They won't crap out on you or anything...I have a Ractive heatshield filter on the other car...and it works pretty well.