What would help my setup sound better ?

Room treatments, better setup especially eq, and a far more serious subwoofer are all strong possibilities.

What don't you like about the sound of your current setup?

I can't find any tech information on the Velodyne Op 12 you mention, but it sounds like its a based on a 12" driver which pretty well limits what it can do.

I'm assuming he means this...

http://velodyne.com/optimum-12-black.html

I am curious about your response as well though since I have a 12" velodyne dls-4000r. What specifically do you mean that a 12" sub is limiting?

The world of subs is just getting wind in its sails with a single 12" in a small box. ;-)

Don't get me wrong my best system at home has a 12" Paradigm sub which is probably a little less competent then the twice-as-expensive Velodynes.

But I have no illusions about it being the end of the line when it comes to bass.

IME bass gets into diminishing returns when the sub has like 4 18" long stroke drivers, each with a killowatt or so driving it.

What would make your system sound better? Maybe an Onkyo 809 or 1009 receiver, replace the def techs with another set of RS-62ii, get dual identical subs from Outlaw, HSU, SVS, Rythmik, etc..... If you go 9.2 get a set of RB-81ii or even RB-61ii for either front heights or wides.