I use an RBH1012 sub with my N805Sig's. I have my cd\dvd player hooked up to an Anthem AVM20 on two inputs so I can turn of the sub by switching inputs. The sub adds a little extra umph but the sound pretty good without.
I owned the 805's about 3 years ago. They do need a little help getting the bottom filled out. The problem I had was getting a sub to blend seemlessly with them. You need a fast sub which generally means a sealed enclosure. However, with the 805's port resonance and phase issues, it was hard to match anything that sounded right. The 805's are fast. If you don't use a fast sub then the bass sounds slow in comparison which seems to distract from the musics pace.
I hope if you go that way, you have better luck than me. I thought the 805's were very nice sounding speakers with an extremely open top end. Just couldn't get the bottom right so they went.