Sony's added a few pseudo-surround modes that you can play around with in the menus to try to extend the stereo width but I found them to be of questionable value. Audio quality was better overall with them turned off.
2D picture quality
As you would expect given its price, the 40HX753 lacks a few of the bells and whistles found on the pricier HX853. It doesn't have the latter's local dimming feature. Instead, it has what Sony calls Frame Dimming. This appears to mean it dims the backlight slightly to improve black levels when it thinks it's showing an image that has mostly darker content.
Motion processing is limited to 400Hz (it's a 200Hz panel with added backlight blinking), whereas the HX853 has 800Hz motion control. It also uses the more basic X-Reality picture processing rather than the X-Reality Pro system on the higher-end model.
It's perhaps not surprising then that picture quality doesn't quite reach the dizzy heights of the excellent HX853, but it's still a very good performer. I'm happy with the picture presets on the whole -- they're much better than Samsung's. The Cinema mode in particular is quite accurate with colour and contrast, and it's a decent option if you're watching Blu-ray movies. In fact, colours in general are nicely dealt with and there's a finesse to the trickier stuff -- such as skin tones -- that's lacking on some competitor models.
As with all LED sets, there's inherent motion blur when all the motion processing is turned off, but Sony's motion processing is very strong. The Clear Plus setting works well for movies, while the slightly brighter Clear mode is a better option for standard TV viewing.
The frame dimming feature isn't anywhere near as effective as the HX853's local dimming. While it tries to work out when the TV is showing darker images to dim the backlight accordingly, it sometimes causes colours to shift ever so slightly, which you may find distracting. Even so, the TV's black levels are quite deep anyway and it's also a good performer with contrast, as it's able to tease plenty of detail out of darker scenes.
Upscaling of standard-definition images and web content isn't quite on the same level as the HX853 either, but the X-Reality engine still does a decent job of cleaning up Freeview channels from the tuner to an acceptable degree.
On the negative side, the set has noticeably tighter viewing angles than those of most other manufacturers. If you sit too far to the left or right of the TV, colours and contrast shift, so pictures tend to look washed out and colours take on a blue-ish hue.
Also, if you're watching the set in a darker room -- say at night with the lights dimmed -- you can see some light pooling around the edges from the backlight. However, I've got to say this a good deal less of an issue on the 40HX753 than it is on some TVs.
3D picture quality
This set doesn't come with 3D specs, so if you're thinking of using it for watching 3D movies, you'll have to factor in the cost of the active glasses. The TDG-BR250 goggles that are compatible with the TV can be bought online for around £40 each.
They're big, chunky and not hugely comfortable to wear. The thicker sides do at least help to block out ambient light and limit flickering in the corner of your eye caused by ambient light sources in your room.
Faster is better with 3D screens as a speedier panel helps to cut down on 3D image ghosting -- usually known as crosstalk. This model is rated at 400Hz and although you can see a little crosstalk creep in here and there, it's not hugely noticeable and doesn't distract from the 3D experience. In fact, 3D images look sharp and, despite the dimming effect of the active glasses, retain a fair amount of punch in the brightness department.
The 40HX753 isn't an outstanding performer in the way the more expensive 55HX853 is. That said, as an overall package, this is still an impressive model. It has an affordable price tag, strong picture performance across both 2D and 3D, and support for a wide range of smart TV services. Only its slightly narrow viewing angles and failings with digital media playback blot its copybook.