thank you very much for your detail response, it helps me a lot.
but i still want to give it a shot to try how these bass shakers works. (since i bought it on ebay, there's no returning). your opinion is right, getting a sub woofer can definely get me the sound quality i want. but considering the space inside the vx is so limit, i really don't want to waste any inch of the space. so i am going with these bass shakers.
you mentioned the TOD system is right underneth the front seats, so if i want to install there, how can i avoid damaging it? or how can i know where it exactly locates? is this the main problem i need to consider due installation? or are there some other places i need to pay special attention to? Thank you.