here's diagram for Audyeesy DXS placement of speakers .there is some debate on RS over RB here & most of that is preference & what your room is shaped as.
the RS surround speakers depend on reflecting the sound off the walls & objects then back @ your ears
the RB's are called direct radiators & are to be aimed directly @ the M L P (main listening position) so that the sound is direct from speaker to your ears .
your Front towers the 82 's are direct radiators Also .
the RS's work well in long narrow rooms (where the left / right/ center front speakers are on the shortest in length wall in the room ) where seating is in rows or as backs( in a 7.1 system) if the seating is at the back wall as in a couch
look @ the RS's, the horns are @ 90 degree angles from each other (Klipsch calls them Wide Dispersion ) but they are bi-poles (google,WiKi bi-pole speakers to better understand their use ) AND they are more expensive as well over what a similar direct radiator in the same level of bookshelf speaker will cost .
****the 51's will NOT be timbre & voiced matched well with the 82's due to the horn much different & way smaller****
I suggest you step up to the RB81's as they are the same price as the RS51's as with a 81 you will be getting a much bigger woofer than a 51 & the horn is voiced matched to the 82's as it's the SAME horn ! .
it's important that with a 5.1 system that all speakers be voiced the same & have the same timbre ,if in the future you add speakers say to 7.1 or 9.1 you can add some of smaller speakers but I'd try to keep the set as closely matched there also as then you will experience a room that has total envelopment of the sound of music & Home Theater as in movies & TV . & that is best described as being on stage with the band &/Or in the middle of the action movie when U feel that things are coming @ you from all directions ( Say ; gun fire coming from one side of the room, the bullet whizzes buy your head & then impacts on the opposite wall)& You NOT knowing or realizing which speaker any of those sounds came from at any given moment , That Is A Total Envelopment Experience, And that is what Home Theater is all about making your room a better sonic experience than going to see a Film at your local CinemaPlex.........
Of course I must add a disclaimer here ....
This Is I M H O ....... but I have been down this road before & had wished that someone had explained it better to me THEN.
As then I would not to have had to sell & replace speakers to get what I've got now a well voiced & timbre matched set ...
i learned thru trail & error & yes I did buy speakers that I wished i hadn't.
money is best spent if you are knowledgeable on how your room works & How the various speakers will work in your room .
Might I ask what are the wall lengths , where the center & display will be placed , what AVR you will use ? is the room filled with windows , are there any large openings to the HT room that lead to other rooms (like dining room, kitchens ect . ? )
Is your Home Theater room the living room or is it a dedicated Home Entertainment room
I ask all this to better help you , many members here have vary different rooms than mine & we all can relate our own experiences with our various rooms in some way to help with what you ask . We can better help by knowing what you are dealing with .
I my self have a living room the wife has let me do what i want with placement of speakers & put any size speaker i want where i want ,but it is a living room with a large opening to a dining room
the living room is 24 feet by 20 feet with the display @ the center of the short wall meaning that it's wider than longer , with a huge picture window on the right side But has a heavy thick curtain so not to reflect sound & the opposite wall has on it's full length bookshelves that act about the same as the curtain does