More Power or use subwoofer to boost bass for music

That's Fletcher Munson equal loudness curves you're talking about. Duke has said pretty much the same thing. One consequence of this is its important when setting sub levels to do it at a level you care most about. 

I use matched amps and pre-amps for my older 803's and subs. This gives me control of the bass without creating out of phase signals. It also allows me to tailor the bass for the recording.  Many old albums really open up when the bass is not relegated to a recording mixed for what a 1960's 35 wpc amp could produce, or a modern AVR receiver.  Powered subs with frequency roll off controls, as well as tone controls, alter the phasing, thus negating B&W's primary design philosophy.  They are also hard to adjust for each recording. 

Also, you might want to use your amp for the subs, then get a less powerful amp for the 804's, if price is a consideration.  100 watts will easily power them, as long as you are using subs.

danvignau:”I use matched amps and pre-amps for my older 803's and subs. This gives me control of the bass without creating out of phase signals. It also allows me to tailor the bass for the recording. “

     If your tailoring the bass for individual recordings, that indicates to me the subs are are either not positioned properly in relation to the listen seat or the primary controls on one or more subs, volume, crossover frequency and phase, are not properly set.  Setting these 3 primary controls properly on each sub is very important for seamlessly integrating subs into a system and room, just as important as properly locating each sub in the room in relation to the listening seat.       It’s also usually the most time consuming step When incorporating subs into the system and room.  This is due to the reality that a good sampling of musical tracks, of different genres and containing significant bass content, need to be played to determine the optimum settings on these controls that provides the most natural sounding bass.
     If adequate time is not devoted to thoroughly completing this step and arriving at the optimum balance of bass settings for all subs that sounds very good on all music genres listened to, individuals may feel a need to adjust these settings prior to or even during playback.  Who would willingly accept doing that?

Tim 

I’m using a pass labs xa25 to drive my 804 d3s. No problems with bass. The bass is controlled, deep and detailed. The xa25 loves pushing those loads being stable down to 1 ohm along with a damping factor of 500. Positioning from the front wall was key for me also. The bass power would vary by each 1/4". It took time to dial it in. Literally, 3/4" was the difference between too much bass that began to smear the mid-range slightly to having the perfect bass for me. My speakers are toed in, so measuring from the inside corner of each speaker to the wall is 31". (30.25" was too much bass, 31.50" was too little bass). Measuring from the tweeter to the wall perpendicularly is 33.5". Measuring in parallel from the tweeter to the wall is 35". I do use bass traps on the 4 corners of my front wall. I have no need for rear bass traps because my back wall is 35’ away. I also use isoacoustic Gaia ii for the 804s which tightens up bass. This is my experience with the 804s.