I want a decent sub but am seriously constrained by budget and size restrictions. I picked up the Sony SA-WM40 for $150 based on reviews. Well that thing moves an amazing amount of air for a $150 subwoofer. But it isn't particularly tight, fairly boomy in fact. What do I expect at that price, right? Well I was wondering - can I purchase a new driver like the Adire Shiva driver ($135) and pop it in for better performance? If so, what is entailed? Is it easy or involved? A website link for DIY subwoofers would be appreciated. Also, I was thinking about addressing the boominess by filling the cabinet with polyfill. Is that a good idea? One final question, is it OK accoustically to put a subwoofer on its side? I need it to fit under a couch end table and it barely doesn't have sufficient clearance. But it fits if I turn it on its side.