Subwoofer concern

[Carlsberg19]

I just bought a new speaker system, see HT Gallery, and i have a concern about the subwoofer almost to the point of thinking about getting a new one, for startes the sub isnt completely level on the ground (and the surface it is standing on is perfectly flat) so it rocks whenever there is a bass heavy scene and causes a really irritating vibration, resulting in me having to mess about with the LEVEL and BASS BOOST options on the sub.

The other concern i have is it is a downward firing sub, and i was so used to my forward firing sub i had before, but this sub just sounds empty and hollow and does not give me the bass i want,

So im thinking, i could just place the sub in a corner somewhere and secure it againt a banister so stop the annoying vibrations or else get a new sub, what u guys suggest