When you say it is wired, what exactly do you have in place today? Do you have loose wires at each potential speaker location? Or do you have panels in place with speaker plug ins ready to connect a banana plug? Or do you have wires behind drywall somewhere?
Same question for your TV. Is there an HDMI cable run through the wall from the TV mounting location to wherever you would put the receiver? Or is there conduit in place to run that cable through?
Finally, is there a panel near the receiver location to connect all the speakers on that end? Or at least loose wires that are labeled for location?
For the surround speakers, are you looking at doing an in ceiling or in wall speaker? Hanging a traditional speaker? Or just setting them on stands or a table or whatever?
These are the factors that will drive the ease of install. If all the wiring is accessible and clearly labeled, this becomes largely plug and play. Sort of like connecting monitors and accessories and firing up a new PC. Speaker wires to the appropriately labeled ports for your sound, then HDMI to the proper inputs for you sources, then an HDMI out to the TV. Done.