it will only affect the surrounds, and rear surrounds. The short version is, the decoder will extract what is deemed appropriate for the rear surrounds from the side(normal) surrounds. Since there isn't any "coded" rear surround information, it has to come from somewhere. The problem is sometimes it puts sounds in the rear that should only come from the sides. It's matrixed surround, like how the old dolby surround used to pull ambient sounds from the soundtrack for the surround speakers. IME, it just doesn't work, and if you are at all fussy about surround imaging, I think you'll find the same thing I did. I do still enjoy native 7.1 tracks played back as such. I just feel that the old upsampler doesn't work. For some music though, I like plIIx. It can be kinda like a sci-fi film track, with electronic sounds coming from all over the place. I'm really curious as to your findings after some quality seat time.