In some respects, being open plan can help the sound. Bass boom is less of a problem, and sound reverberation issues can be reduced too. On the flip side, it can be harder to generate a decent/high sound level, so if you want to replicate the huge sound of a commercial cinema in a smaller space then it's going to be a bit more of a challenge, particularly with smaller speakers which are less efficient than bigger ones. That said, as long as your expectations are realistic, then you can get some really great results.
Before we go any further, in a 5.1 system, the surround speakers are meant to go on the side walls rather than on the back. It's not the end of the world if they go on the back wall, but it's not where the Sound Engineer who mixed the sound track expected the speakers to be.
Before we get to 5.1 surround, I'll write a little about the sound bar options.
At the sort of budget you're thinking of spending, then you'll have some pretty decent choices. You've probably already worked out that a 2.1 system is effectively stereo speakers in a single bar-shaped cabinet, plus the sub which accounts for the ' .1 ' bit of the 2.1 description. A 3.1 system adds a dedicated speaker for the centre channel which is mainly where voice is mixed to. TV programmes, movies and such can have their sound mixed down by the TV or the sound bar to suit the number of speakers available.
Once you get above 3.1 then you're in to the surround sound versions of sound bars. Some use 'wireless' rear speakers which, in most cases, aren't really properly wireless: There's either a small secondary mains-powered amp plus speaker wires to the two surround speakers, or one of the speakers has some amplification built in and it then runs the second surround speaker connected by some speaker wire.
The other increasingly-common option is the ATMOS sound bar. This is where the sound bar has additional speakers built in that fire sound upward at your ceiling with the objective being that it bounces down and replicates the effect of in-ceiling speakers. I think that whether Atmos would suit you depends on the material you watch (is it Atmos encoded); whether your room layout puts you in the correct position for the reflected sound to be effective; and - most importantly - how you plan to hook up all the gear. You see, running everything through the TV first before passing the signal to the sound bar makes life convenient. The catch is that very few TVs can pass Atmos-encoded sound to something such as a sound bar.
Atmos might not even be on your RADAR, but maybe you still fancy good surround from a sound bar? There is a way.
For a long time now, Yamaha have been doing a special line of sound bars that use this idea of reflected sound bounced off walls. It's the Yamaha YSP range. The company knows a hell of a lot about room acoustics, and they've combined that with a clever multi-speaker array that can target sound to hit a specific point on a wall so that it bounces off at the correct angle to hit a listening spot. Doing this, they can create a believable acoustic facsimiles of the surround speakers of a 5.1 system. Before you get too excited, you have to know that the room has to be suitable to get the best effect. It needs a certain amount of open uncluttered wall space for the bounce effect to work.
Aside from speaker configurations (2.1, 3.1, 5.1, Atmos etc), the other factors to think about with any surround system is the connectivity and what formats it can handle.
I've already covered Atmos and the potential limitations of connecting via the TV's audio out (optical certainly, and very possibly HDMI depending on the TV model). The things you play through any audio system can have a variety of different audio tracks. Stereo, Stereo with Dolby Surround, and Dolby Digital in anything up to 5.1 are the most common. However, there's also DTS and the high-definition audio formats of Dolby True HD and DTS Master Audio and audio with the enhancement of Dolby Atmos. Put most of this through the average TV and it won't know what the hell to do with it. What you end up with then is the fallback of the lowest common denominator audio, and that could be a very low-tech and low-Fi Dolby Surround. This is why connecting sources to your TV first can be a bad thing, and why having plenty of sockets on a sound bar or surround amp turns out to be a very good thing. This, and the ability to decode those audio formats so that you get the best sound signal regardless of what's playing is one of the big advantages of a really good sound system.
Since we've now started to think about how things are connected and what that can mean for sound, then it's time to introduce picture in to the equation too.
TVs has gone 4K UHD, and with that there are video sources that use the extra features that the format offers. 4K UHD Blu-ray disc is still top-of-the-tree for quality, but you can also stream 4K from Amazon, Netflix, Youtube and there's content on Sky Q. To make sure your system has the broadest compatibility then the HDMI sockets should be rated to accept HDCP 2.2
Let's wrap up with some equipment recommendations for a 5.1 system.
For small speakers that actually look good and - more importantly - sound really good too, then I don't believe you can go too far wrong with the Monitor Audio Mass system. It's available at £499 with a matching sub, or just as the 5 small speakers excluding the sub. This provides folk with the opportunity to pair the satellites with a larger and more powerful 3rd party sub.
Looking at AV receivers, if you don't need Atmos features then the Marantz NR1509 @ £349 ticks all the rest of the 4K UHD boxes, and the receiver is very compact. Where you're looking for Atmos, more power and more features then AV receivers in the £400-£700 range will probably cover your needs. Look at Sony, Yamaha and Denon.
