If I was you I would be looking along the lines of Genesis, Phoenix Gold etc. If £1800 is your budget then you could have one hell of a system, as dualmono says I have never heard a stock system sound as good as a bespoke even if it is supposedly Bose etc. I think that is more of a marketing ploy if I'm honest as Bose home audio is fantastic.
I have just got my A3 and it has a Bose system in it, although it isn't a touch on my complete Genesis system in my Focus I think I will leave it be as it must help with resale value having Bose but I might add a sub for a bit more bass.
That said, I *might* be selling my Genesis kit from my Focus. If I do I will put it in the relevant section on this board as well as TalkAudio (a fantastic ICE forum).