N802 + Velodyne DD-18???

Srdan01, My room is about the same volume as yours and a DD-15 does fine for me just filling in below 30Hz. However be cautious, as current Vel 2.2 software only allows crossover at 40Hz and above. Unless you can get Velodyne to FPT you the older 2.1 software, you will have excessive overlap between the sub's LPF and a full-range main speaker. Using the sub's EQ to fill in null points much above the crossover point is usually a bad idea.

Any Vel DD can be improved with a few internal mods to the plate amp & wiring.

I actually planning to build new box for DD-18. Goal is to look like hi-fi stand (invisible) with down-firing base driver, like Rel.

I am using 802d's and an HGS 15. THe Velodyne seemlessly covers the lower bass that the 802's cannot reach. I concur that weight on top is a great idea. I use a Bright Star Big Rock/Little Rock sandwich.

Srdan upgraded his speakers to Jamo R909