Upgrade B&W CM4 to what?

I have a Yamaha sub in the mix also but I’m very fickle in using it. Sometimes it works for what I’m listening to and sometimes it doesn’t. The room is very sensitive to speaker placement. If a switch the wall that the speaker is aligned to, it sounds like the music is coming out of a little box. Placing it along the long wall (18” from wall) totally changes the sound. This is where I have it. The lightest toe in or changing listening position changes the sound.  Based on what I am gathering from comments is that the thing I should do first is master the acoustics of the room using what I have and then upgrade. Right? 

Have you considered adding a subwoofer or two?  I also have the CM4s and lime you I wanted a fuller sound.  I added a Sunfire Atmos XT, and then eventually a second identical sub.  I bypass the crossover on the subs and run them without a ton of gain, the result is nice tight ample bass.  You could get a decent subwoofer with your budget and achieve that full sound.

I like the clarity and stereo imaging I get from the CM4s, they don’t make them with that full front aluminum baffle anymore, and style wise they look very similar to the newer 703 S2 with the grills on.

Anyway, good luck, I’m curious to know how it works out. 

Vintage speakers like mine, the crossovers were designed with L-Pads at mid-attenuation, which allowed boosting or cutting the mids relative to the woofer and boosting or cutting the highs relative to the mids. I just used a sound meter and a pro’s ears to adjust mine very successfully. You could adjust mine to your space/ears very happily in your space I am sure.

This was actually before stereo, the great mono designs which were often subsequently doubled in spaces when stereo occurred.

They anticipated unknown spaces to range from dull to bright, and for personal taste, in your case personal needs also.

Very few modern speakers allow adjustments, a shame IMO.

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You might want to think about a good graphic equalizer which would allow more specific attenuation (boost or cut) than tone controls. Perhaps a used one with return privilege’s.

Then, mess/learn how to use it with your existing speakers first, next consider what speakers you could thus have some specific control of.

Oh yeah, I found my inexpensive sound level meter and test cd with specific tracks of 1/3 octave frequencies great tools. I realized, I don’t need a pro/accurately adjusted one, just answers of relativity of each adjacent band

tripod, seated ear height, listening position

there are others, this test cd has 29 selectable frequency bands

If you decided on the B&W 800 series speakers, you may need to upgrade your power amp as well to take full advantage of them. 

Try SVS ultra towers sounds great with my Krell FPB 600

yeah, then lots of choices

https://www.usaudiomart.com/search.php?show_other_marts=N&keywords=&type=ALL+SALE+ADS&search=Search&type=ALL+SALE+ADS&cat_id=26&price_min=800&price_max=1450&province=&photo=on&zipcode=&radius=100

I would stay away from the luxury brands

I would add that I am interested in used speakers.  

that's a difficult price range for new speakers. I spent 4 months trying to find speakers for that amount and finally gave up, and jumped to $1600. (Happy ever since) Crutchfield and Safe & Sound has open boxes with steep discounts that might help

As a former owner of the B&W 703s I can tell you respectfully the B&W CM4 is a bad speaker. I went from the 703s to Thiel 2.4 (no longer made several pairs on here used) and the Thiels made the B&Ws sound broken. I paid about the same price for both. New for the B&W and dealer demos for the Thiel 2.4s. I still have both these speakers around and others so these comments are not from memory. 
 

Anyway shop the used market. You can pick up older $3000-$5000ish speakers used here in your budget all day long. klh model 5s have been getting great reviews at only $2000 new. I imagine a used pair would be a good buy.