Recently purchased a Pair of KEF Q900, and a Q600c at waht I consider fantastic prices due to the new models and clearance of the old stock. Upgrading from a little Tannoy HTS101 system which has been great, that was a downgrade 4 years ago from MA BX5 setup to clear floor space due to a little one crawling around. So over moon with these and being back into full range setup. So now I am considering a Sub purely for movie usage. Looking around £500ish budget and towards a BK option. I do seem to suffer with some horrid acoustic room modes and nulls for subwoofer performance due to having an almost L shape room and without the sub sitting in the near middle of the room which isn't an option, can't resolve so have to have the happy medium. Acoustically, I don't seem to suffer the same problems with speakers whether small or large, so I would assume placement is the real issue. However, my options are limited. I assume these sound issues will only be emphasized going with a bigger more powerful subwoofer unless placing correctly and clearly a larger box will reduce placement options even further meaning that to EQ flat, I would be limiting the overall performance advantage anyway? In this situation and from research, I gather that I would be better with two to help smooth this out and that a sealed box will also help? So this brings me onto if two Q400b would be a good or better choice for the price. There is little in regards to reviews on this model. I am particularly impressed with the Q900/Q600 performance and being a sealed unit imagine this will also have an advantage of working well in a system used primarily for music. Although I don't really consider this as a major factor in my decision as the performance is perfectly acceptable from the mains alone and I always run direct mode. I accept that the single BK Monolith or XXLS400 will rule a Q400b and that at a £500 price point there are alternatives such as an SVS that may well serve better than the KEF in a single application. If it was a single subwoofer purchase I would most certainly be looking at the aforementioned options. But, essentially if having two units will solve some of my issue, I can't stretch the budget to £1000 to have two of those 'preferred options'. So will the heavily discounted Q400b be a contender, should I consider a couple of the smaller BK Gemini II instead which is cheaper overall or just go with a mono,XXLS400. Adding an additional Monolith or XXLS400 isn't an option due to WAF. Convincing her to have one sitting in the room is going to be hard enough.