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

You may be able to land a pair of Maggie 3.7i used or the 1.7i with a good sub would also be worth auditioning.

Good luck happy listening.

What about used ATC SCM 40s?

ATC are the most accurate speakers, imo. See if you can stretch to the SCM19s ($4700) otherwise the SCM12s

Later add a Dynaudio 18s sub  (~1800)

ATC are a dominating presence in pro recording studios

https://atc.audio

Your B&W are a perfect match for the McIntosh amplification.  However they can be a little stogy in the midrange.  

Another excellent match with Mac amplifiers are the Klipsch Heritage.  

The Forte IV sound excellent paired with your amplifier.  The Forte IV has a lively deep and rich sound and is the more refined than the Heresy.  

Be prepared for a more exciting sound and much more life like midrange,  

Should be able to find new under your budget.