In that line of thought, if all of the equipment in your sig was what I owned, I'd be researching subwoofers. The toughest part would be in deciding to get the best I could afford, or sacrifice in order to go dual. However, I need to fill a lot of volume at close-to-reference SPLs. OTOH, your sub does seem to have a decent rep I suppose . . . but so do your speakers . . .
The next toughest decision would be between upgrading the sub, or getting room treatments. But, that decision might be a tad easier as I'm pretty sure I'd get a nicer sub for my own room. If you have a smaller room, go with treatments. Or maybe throw in a nice remote. Or some nice HT seating. Wet bar. Mmmmm.... wet bar.... :drool: