Where is the bass on my B&W 802d speakers?

Acknowledged. I have the 801’s which have a single Woofer. No one said it would be easy. The gear purchase is often only the beginning of the journey. 
 

I remember one presentation from Dyne Audio (I think) that mentioned a typical bass frequency sound wave was 30’ in length which means that unless your room is at least 30’ deep, the sound wave ‘high’ will bounce back and either reinforce the succeeding bass note ‘highs’ or level (nullify) them. The subwoofer’high’s and ‘lows’ are frequency and distance sensitive. Avoid offending bass frequencies, no nullification; move to a different distance from the speaker (or the wall), and again, the nulls disappear. It is these facts that any solution must address. 
 

Bass traps, ‘catch’ the rebound signal off the back wall, and solve the null problem by preventing the interaction. Seems a cleaner solution to me, but I listen near field at the moment, so I’m not experiencing what you are right now. 
 

Again, Good Luck. 

It seems to me that you can test the Room Null theory by walking around the room. If there are nulls, there should also be points of boost, where the bass is accentuated. As is pointed out above, there isn’t much you can do about how the speakers perform in the room without major re-orientation. For instance, if they are on the 25’ wall firing in at the 16’ ft wall, put them on the 16’ wall and fire them at the 25’ wall. 
 

The reason subwoofers help is that you can move them around the room. Put the subwoofer in the listening position and move around the room until the bass is strong. Then put the subwoofer in the place where you are standing and the bass will sound strong in the listening position. The subwoofer, by being in a different position in the room, counteracts the room modes generated by your main speakers. 
 

Some people find they need, two, three, or four subs in an ‘array’ to fix the problem you are having. 
 

I responded to a quiz recently, is it the room, the speakers, or the amp that makes the most difference to sound quality; 62% responded that it was the room. It truly is a limiting factor, or, shall we say, the biggest opportunity to improve sound quality. 
 

Good Luck