Very interesting deal there.
But beware.
You would be buying way way more speaker cable than you are likely to need. This means you spending money you don't need to spend and you're adding too many meters to you run lengths. This will not do the sound any good.
Check what you actually need in terms of run lengths and request shorter runs and an appropriate amount off the deal price.
Now, for the onkyo £1000 is probably what you'll have to pay, but the Dali set should come in around £1950 plus delivery if you have to choose it. the setup fitted easily into my small estate car in one go.
Cables, you can probably do better negotiating this seperately. But see what Creative will do. You'll need two HDMIs one from your playstation 3 to the Onkyo and one on from the Onkyo to screen. By all accounts you shouldn't use the PS3 HDMI cable but upgrade it. You don't need a coaxial cable or a stereo analogue cable. So you can save the money from those.
You can run the 875 bi-amping the front pair, so if you don't go for a 7.1 set-up, don't get speaker cable for the front pair, 2 sockets to 4 sockets, that's bi-wiring, get 4 to 4 which will allow bi-amping.
Post again if any of that doesn't make sense.
I think you need to put a spreadsheet of your cable needs together. It gets complex and you need to be sure you've ordered exactly the right stuff!