Hi Kirky1980, your KefLS50's would sound wonderful in a HiFi setup, with something like a Roksan Kandy integrated Stereo amp and maybe matching Kandy CD player.
There are lots of options to choose from and will give stunning results with the right associated equipment.
However, if you expect to get Hi Fi quality from an AV amp, you are likely to be disappointed, especially at £500.
Most AV amps are designed as Multi input control preamplifiers with room equalisation incorporated into the signal path, plus equipment to deal with video processing and upscaling etc.
Then they fit multichannel output amplifier stages and a power supply all in the same box and give great performance in home cinema applications for which they are designed.
But if you want to maximise the potential from your speakers, you need as little signal processing of the source as possible and a power amplifier that has High Current output stages, backed up by a power supply that has energy to spare, with minimal distortion to control the drive units in your speakers.
Most AV amplifiers generally cannot give Hi FI performance.
However, some AV amplifiers have room correction circuitry that can electronically compensate for the poor acoustics in your listening room, which despite having that added circuitry in your signal path, may sound better to you than if you listened to your speakers on a HI FI system without it.
The Power amplification in most AV amps, however, in my experience is generally lacking the grunt required to drive good quality speakers to Hi Fi standards, hence the fact that many people use additional separate power amplifiers from their AV amp Pre-Outs or separate room processors.
The only AV Amps I am aware of that are capable of driving speakers to Hi FI standards are those made by Anthem as they do have proper Power supplies with big transformers and state they Draw more power from the mains than they claim to deliver to you speakers, which is always the case with good HI FI amps. They also have the best room correction software on the market.
If you want to go the AV surround sound route, but still wanted to play stereo music then my first Audition would be with an Anthem AV amp and you are looking at the higher end of your budget.
Also be aware if you are planning to use a Blu Ray player as your Cd player, consider auditioning a dedicated CD player too, via analogue and digital outputs.
Have fun, sorry if I have confused you.