Crossover frequency

If your 805s go down to say 50hz in room -3db, then you shd X them over below that freq, about 40-45hz. There will be some overlap between the sats and the sub. The idea is to find the right spot so that these's a smooth transition between both spks.

I'd recommend you play various types of music, pop, rock, classical, jazz and tune the Xover till you can listen to any type of music without having to adjust it.

The sub should not draw attention to itself.

Test tones and an SPL meter might help. Set your sub to kick in where your B&W's start to roll off. Even though you might have sound down to, say 35Hz, they might be down 10db at 35Hz starting at 50Hz. If this were the case, I'd set the sub X-over at 50Hz and set the gain to maintain the same SPL as far down as your sub will go.

Try cutting one octave lower -- i.e. 40Hz. Listen carefully. Sound should be "fuller" but realistic and nothing should be bigger than life, i.e. a cello should NOT sound like a double bass, a viola like a cello, etc. If it's too light sounding, go up by 1/10 octave until you get it right. If the opposite, go down by 1/10 octave.

Do you know how sharp the Meridian x-over is? It might help.