Just my initial thoughts on two subs in my set up now. I bought a 2nd REL Q Bass and have now integrated it with my system. It's been 'in action' about two days. The sound seems to be more fullsome. The mono bass effect of one sub has definately gone, but it wasn't bad in the first place, just better now. There is more depth and less thud. Sounds do seem more realistic, ie, glass tinkles better when broken, raindrops are more solid, whooshes and whishes etc are more 'there'. It's dificult to quantify or explain, but the differences are there to be heard. The amount of bass is not really what I'm on about, but the quality of everything. Anyone can pump up an active sub and blast the glass out of the frames. One way to describe the overall sound is it's easier. Now I bought the sub 2nd hand. My room is 12' x 11'. I have to consider things before moving it around, ie, domestic, cosmetic and practical reasons. I have neighbours to consider. Taking all these into account I'd say I have value for money. If I'd bought a new sub, then maybe not. (The price paid wouldn't with overiding ease justify the gains). My room and set up would survive very well with just the one sub. The moral being to definately try before you buy. The room is without a doubt the biggest single influence on how a 2nd sub would integrate into your system. Ok, I gambled on another one and it seems to have worked nicely. I can get away with messing about with stuff like that, the wife understands, honestly. So if you are thinking about it, it is worth a go if you can accommodate another sub easily. But if you already have one high quality sub, in say a room like mine, then get a demo. You may be better off spending your money on more cheesy films instead.