How far back from the front speakers will the couch be? Unless your seats are all the way against the back wall almost any loudspeaker with 5.25" or 6.5" woofers should be alright.
Paradigm Atoms (google some reviews, they are universally beloved budget speakers) and CC-170 will MSRP at $400 for both (which is my former set-up, very nice.) When your budget allows for surrounds and rears just buy more Atoms or the slightly more expensive ADP-170 surrounds.