New to home theatre ish

Sound bars have an interesting effect, but they're not really proper surround sound. They also tend to have one 'hot spot' & can sound distinctly weird if you're sitting off-axis.

We've got a Yamaha soundbar in the kitchen & it improves the sound from the Samsung TV considerably (not difficult)

You've a very good stereo & TBH unless you go for a decent setup you're going to be disappointed. What's your budget?

If budget is really tight then a used Yamaha DSP-800 may suit.  This is a 5.1 processor that provides amplification to centre and rears with a line level sub output.  The fronts are provided by your existing amp and speakers via the unity gain input on your Naim so Just add centre and rear speakers to suit.

I've found the Monitor Audio Radius work well, compact and smooth and easy to install if space is tight, but there is plenty of choice in used speakers.

I've just changed over from the Yamaha to a Naim N-VI which slotted in perfectly and saves me a shelf as it had the built in tuner as well.  Clearly a nice asthetic match for the other components and very compact.  It was buggy at first but a quick email to Naim and prompt response with a firmware update resolved all of these issues.  The Naim N-VI sells for relatively little money if you keep your eye out.

This is all in context of a much more modest system (202/200/NAPSC, Spendor A5)

Richard

OK Gary, I'd go along with Richard's suggestion but it doesn't appear feasible for you to incorporate your present stereo system into a surround setup.

Best plan, if you decide not to go for a Soundbar (and unless you are constrained by placement of the five speakers plus subwoofer needed for a true surround sound system I really wouldn't recommend one) is to base a system round a processor/amp from the likes of Denon, Yamaha or Onkyo, ideally that can decode HD audio. This will have all the amplification on board save for the subwoofer which will generally be active & have its own amp on board. There are bound to be plenty for sale S/H, have a look on AV Forums as well as e-Bay. One with an HDMI input/output would be good.

Then you need a set of speakers, but with a decent amp fronting them, as long as they match and are from a reasonably reputable manufacturer, you'll get a pretty good result. Matching the subwoofer's not quite so important but don't be talked out of a centre channel speaker!

Good luck.