With sound quality, it's a very subjective thing and impossible to write so one can 'hear'...
But in my experiance, I have found that good quality full range stereo speakers will easily trump the sound from a cheap 5.1 set up (especially those with rather small cheap speakers). In any case, the rear speaker channels are band limited in 5.1 encoded audio so they are only good at placing fill-in sounds like bullets bouncing around, jets come in from behind, etc. While some people like these fill-in sounds, i often find it over done as it seems 'action directors' focus too much on the action to the detremant of clear vocals and often plot lines.... Having said that, i still like my action films
As always, with sound quality, the old theory has been to buy the best speakers you can afford, then move back towards the source as funds become available (amp, turntable, etc - ignoring the super duper oxygen free copper cable scams). I believe this theory is still valid. Luckily with modern digital amps, even the ones in the TV's, the amplification is already rather good so replacing those small tiny tinny speakers inside a TV with full range speakers connected to the TV amp will provide a big step up in sound (as compared to the TV speakers themselves). And usually the TV's i've seen have ability to connect external stereo speaker and some even have the ability to further connect a subwoofer
In essence, a soundbar replaces the TV amp and more importantly its speakers with somewhat better speakers and a better speaker enclosure. I doubt the soundbar will have a greatly impoved amp compared to the TV but the speakers and enclosure will be much better and will be what makes the sound much richer. Amusingly, we pay lots for these thin display pannels which can't house good speakers, then pay again for separate speaker enclosures like these soundbars to get what should be have been part of the TV package. It's odd really......
So before i'd buy a speaker bar, i'd check your TV to see if you can connect external speakers to it. If you can, i'd borrow some good full range stereo speakers from a audio outlet and try them at home - you may be pleasantly surprised (even with some small bookshelf speakers). Ideally you should also borrow a sound bar and do a back to back comparison test at home (otherwise find a nice dealer that has the same TV as you and do the back to back in his store)...
As a disclaimer, i have a Pioneer LX509 which came with separate speakers that attached to the side of the screen (as the panel does not have internal speakers). This setup produced sound that was much better that any other brand i looked at and when combined with the Pioneer picture quality, it helpd seal the deal... Now with this TV, i usually have dynamic compression on as it easily disturbs the houshold and neighbours without the compression. The sound is good enough that i have yet to buy a full speaker setup to complement my as yet unused Pioneer (LX86) AVR... A friend also bought a Logitech THX speaker system some years ago that i expected would be utter crap but they were amazing, so much so that every time Logitech released a new THX range since, it would be compared to this old system and get poor reviews.
So always trust your ears rather than a price point or some spec and there is no substitute to a demo (since you'll be the one listening to it for years to come)...