The LX53 is currently available with a free Pioneer Bluray player (BDPLX54) until the end of this month (extended promotion), which you can either keep or sell on, which means you could get a couple of hundred back on the player, bringing that cost down to about £800. Of course, you could also look at the VSX2020, which is identical to the LX53 bar the from facia, and is available for £200 less, which also comes with a free Bluray player (BDP430).
To keep yourself within budget, you could initially go for the centre, front left and right, and subwoofer, and leave the rear speakers until a later date. This will allow you to get the Apex package in a 3.1 setup and stay well within budget. Depending on how large a speaker you can accommodate, you could look at the KEF Q100's for front left and right, the Q200c, and Q400b sub, which would come out around £1200, making either £2,000 or £2,200 in total. All sorts of options are open to you here - for an extra £200 you can get Pioneer's LX73 receiver, which uses their digital ICE amplification among other extras. This still leaves enough to go for their Q800ds dipole surrounds, or even just another pair of Q100's for rear effect.
Also, with a little discount from your dealer, you may still be able to fit a full Apex package in with the LX53, or Yamaha RXV3067. If you want to aim higher with the receiver, you might squeeze Pioneer's awesome SCLX83 in with an Apex 3.1 package and add rear speakers later.....
There's numerous avenues you can take - the first step is to get yourself along to a dealer and having a listen to a few things to see what you like e sound of, and which direction you want to take.