6.1 and dipoles and center channels, oh my!

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dainis
dainis Posts: 11
Went into GoodGuys a few weeks back and saw their Sony STR-DA5ES floor model on sale at a price I couldn't say no to. Besides, my receiver at that time was starting to have problems (I bought it the year before Prologic came out; surround was based on delaying signals to the back -- bfd)

Currently, I am using an old pair of Polk Monitor 5 speakers, bought back in college, and am in a quandary as to how to upgrade my system to 6.1. (BTW, does anyone know or remember what size fuse I should use for my M5s?)

All the satellite systems are 5.1. I could keep my M5s as front and use 3 of the 4 satellites for the surround backs and center (and waste, er, keep one satellte as a spare?!). Or, I could not use the M5s and use the satellite system center for the back center and get a better center for the front. But would the satellites be sufficient for non-home theater/music? Suggestions? I expect to also need/purchase a subwoofer.

Or (a set of options I favor more). . . should I try matching the M5's with the suggested CS245i for front and back center (not too strong for back center?) and with a pair of RT25i or f/x300i speakers for the rear? And if I choose to use the dipole option with the f/x speakers, how will that interact with having a back center channel (need tripoles?); are there any negative impacts considering that the dipoles are synchronized to alternate signal waves and the center back isn't?? And what is the difference between the f/x300i and FX30i; are there significant timbre differences between the various Polk speaker series to prevent mixing and matching? M3II's are also suggested matches for my M5s, but are recently discontinued; should I pursue this option instead?

Lastly, FYI, here are my room setup limitations:
21' wide front and back walls, 14' long side walls, 8' high (suggested subwoofer model?)
TV/AV system against front 21' wall, midway between side walls
Couch 10' from TV (4' from back wall)
Side walls have doorways adjacent to back wall (one is open and the other is the patio door), and about 12' of back wall (on patio side) is open to kitchen area, therefore surround speakers will be high and need to be small (less than 12" height).
R/L surrounds will be mounted on side walls or on ceiling next to side walls, about 1'-2' away from back wall (above doorways).