Advice on new kit

I am a bit inexperienced with this but at the moment i have a Philips
RX3800 all in one surround sound system. I have it hard wired all round
as the the wireless speakers were rubbish.

Anyway its coming to the end for me as i have an xbox 360 and sky+ and
would like to use the optical out of each of these for 5.1 and the
system is only capable of accepting one coax input from other kit, i
tried a cheap optical to co-ax converter and the results were low
quality sound urghhh

My questions is what to get to replace the all in one, i can still use
the dvd player it also has optical out, the xbox 360 and sky+ all have
optical out too so i would need to have 3 optical inputs on the amp.

Budget is around the £300.00 mark

Also whats the best way of connecting it all up to my one RGB scart on
my TV and what about speaker cable recommendation?

Thanks guys

Chris