Advice from Audiogon family - best speaker $3k-$4k

If you can wait until Sheila Berdan is up and running in her new Seattle-area location, she is an Eminent Technology dealer. The ET LFT-8b has gotten great reviews (especially in the UK, but also by Robert E. Greene in The Absolute Sound, and by Harry Weisfeld of VPI, who declared the $2499/pr LFT-8b to possess the best midrange he has ever heard). Too bad it cost $501 below your minimum budget ;-) .

Brooks Berdan thought (R.I.P.) very highly of the ET magnetic-planar speaker line, choosing it as the planar speaker line over Magnepan for his shop (along with QUAD ESL's, and Wilson and Vandersteen box designs). I have both (Magneplanar Tympani T-IVa, and both LFT-4 and LFT-8b's), buying the LFT-8b after hearing it in the shop. For some reason U.S.A. audiophiles continue to ignore this great speaker value.

Unlike Maggies---whose low impedance characteristics prefer a solid state amp, the LFT-8b is an easy 8 ohm load, the magnetic-planar panel itself (which sits atop a sealed 8" dynamic woofer for 180Hz down) 11 ohms, great for tube amps. Two pair of binding posts---one for the m-p panel (housing a true push-pull magnetic midrange driver and ribbon tweeter, unlike the single ended drivers in the similarly-priced Maggie 1.7i), the other for the woofer---makes bi-amping or bi-wiring easy.

What sound are you looking for exactly?  Sf and B&W are polar opposites as others have mentioned, especially the 800 series B&W.  I've owned both and love the older B&W sound, 800 series are just too bright for my liking. 

At 3-4k you can get used Sf Sonettos and Sf Cremonas, both are exceptionally smooth speakers that are a bit shy on the bass.  They wont be nearly as detailed as your 804s, and with a mac tube pre they might be a little too smooth.  Personally I found that combo a bit too smooth for enjoyment.  The higher end Olympicas are much more detailed and made for a better match for mac tube gear (I run C47 w/ mc275 monos).  

Personally I find Focal to be a great match with McIntosh tube gear.  I've heard the Focal Aria 938 w/ a MA252 and it was an excellent combo.  Like the B&W speakers, I find the Aria line to be too bright but the tube front end rolled it off just enough to be not annoying.  I currently have the Kanta 2s and extremely pleased with them paired to my mcintosh stack.  

Now if you want something completely different from the B&W speakers, try Kef.  Their R series at that price point as very neutral and produce a huge sound stage.  I've heard the R11s on a MA252 plenty of times and it's a great combo.  

You should tell us what music you're listening.

I don’t want a bright speaker.  I like warm, but not muddy.  I need bass and detail.  I don’t see adding a sub with this system. 
I am not opposed moving the 804s and getting a different speaker for the main listening room. I have always wanted a of Maggies. 

I don’t think there are any "best" speakers out there. Some may suit your room and taste better than others.

Other brands you can try is Dynaudio with Emit 50 or 30, Fyne with F502 or F501SP. Canton also has good speakers. Or any used speakers that used to cost $6k to $8k.