I bought a pair of R40's, was going to upgrade them to the 600i's but apparently was a day late missing the sale. Due to the $300 difference between the two for a pair, I've decided to stick with the R40's for now. The question comes in when considering the center channel. According to Polk, the 175i is voice matched to the R40's, the 245i is matched to the 600i's. According to Crutchfield the 245i will sound "fine" even though the better choice would be the 175i. According to my local non major retail chain I won't be able to notice a difference. They said that the 175i and the R40 use the same tweeter, while the 245i uses an upgraded tweeter. They recommended I go with the 245i, spent time to let me demo the two and offered the 245i for $139, ten dollars more than the 175i. On top, they offered me 60 days, rather than their standard 30 days to exchange it for a 175i if I wasn't satisfied with the sound. I am, of course, now completely confused. I realize the 60 day exchange offer basically says to just take the 245i and try it for myself because I have nothing to lose. But I'd like to know a bit more about voice matching simply for knowledge sake...What makes two speakers voice matched? Is it the type of tweeter? The size? What exactly does "upgraded" mean? As I demo'd these two center channels at the store today, I have to say I noticed no difference, other than the 245i performing distortion free, which the 175i didn't do. Anyone out there willing to give a newbie a lesson on the ins and outs of voice matching?