Are you swapping it at a retailer or something? What size room are you listening in and how loud do you listen?
I owned a PV1 (original version) a long time ago and while I agree it's a tuneful sub, it doesn't really have any authority at all below 30hz (based on the old PV1). When I upgraded to an SVS PB12+ the price was similar at £920 but that's where the similarities ended.. the PB12+ was about 4 x the size and it bettered the PV1 in every department. My point being that if you're after performance over aesthetics then you could probably do a lot better than what you have now.. I'm sorry to say that (based on my experience with the older model) if a PV1D is £1200 then I'd be confident enough to say that a single SVS SB-2000 or a BK XXLS400 would wipe the floor with the B&W and even at half the price
http://www.hifix.co.uk/speakers/hi-fi-speakers/subwoofers/svs-sb2000-subwoofer-18648
http://www.bkelec.com/HiFi/Sub_Woofers/XXLS400.htm
I've never heard the ASW825 but I would imagine that being considerably better than the PV1D. Are you limited to certain brands with a certain retailer ? (assuming you are retailer restricted)