You are right, it is a large area to fill, but surprisingly it doesn't take a great deal to get some decent bass to come through, I am not overly interested to have nightclub sound/ volume, just enough to make the music and movies sound good by providing the lower end a bit of a boost.
I am in New Zealand and I would assume that we are limited as to what we get here, but I do know that all major brands are sold here. My budget is hard to say as I am a "buy what is necessary type" but at this stage I would say that the Velodyne spl-1200u is my limit. It is $2999 here which in US dollars is around $2500us. I know that the same sub in the US goes for around $1000us, as to why the difference I don't understand.
Anyhow hope that gives some idea as to what I'm after and what I can spend etc. Appreciate your advice.
At Spyboy - I do agree with your comments, and this is why I am looking at the Velodynes. They are sealed boxes, high output amps (1200w) and are renown for making good subs.
I guess my main issue is that the system I have (Marantz SR 6004 and Kef IQ70s) is that there is a mid-lower range issue. It sounds beautiful on it's own, (but ligtht on bass) however when you stick a 12" sub in the mix you feel there is a bass gap between the sub and floorstanders. This was evident when I tested a friends 12" yesterday. It sounded great for bass heavy tracks, and even acoustic music and classical, but pop or even rock where punchier slightly higher freq bass is coming through the system fell over. This is why I was starting to think of getting a 10". I have tuned my system the best I can get it, even had some professional help, it's a characteristic of what I have and not the settings.
All that said, I take your comments on board and think it is something I'm leaning to doing.