Set up the rear speakers last night. Compared to the upfiring speakers, the rears obviously produce distinguished/isolated audio that can make it sound like there is something to my back-left, my back-right, and even directly behind me. Love it. The upfiring speakers, on the other hand, can make it seem like the audio is coming from the ceiling above the TV, but not anywhere close to directly above my head, which is expected. I will say that the upfiring speakers are definitely a nice cherry on top to the 7.1 surround sound; enough to really wish it supported DTS:X. I'm happy with the SQ, so I've decided to keep this set-up rather than risk not being satisfied with the Z9F. Also, the Z9F would only be $100 less than the SK10Y, considering their rear speakers cost $300. I'll just have to live without object based audio when playing DTS:X movies I guess.
BTW, the prepackaged box for the SPK8-S (at least from Best Buy) doesn't come with wall mounts/brackets which are supposedly sold separately, but even the LG live chat wasn't able to help me find them anywhere for purchase... not even a model number. b&h and beach camera's websites say they come with the mounts though.