That's something that is difficult or impossible to quantify (as in "it is 7.42 percent better"). The 990's lower noise floor does help in all modes, including Dolby Digital and DTS processing, and depending on the speaker setup the quad crossover and discrete channel delays may also yield some improvements. I've been completely satisfied with my upgrade from 950 to 990, so for me it was worth the upgrade. I'm also making use of some of the extra features as well, though, which certainly helps justify the upgrade in my case. However, the fact that I have been able to (pretty easily) justify the upgrade in my case does not mean that the same will hold true for everyone. If you were planning an upgrade anyway, the 990 certainly warrants a place high on your list of candidates. If you weren't planning an upgrade but find the extra features appealing, then you might want to take one for a test spin - there's always the 30-day return policy if you can't justify the upgrade in your case.