We noticed the same improvement when we upgraded from an Avant to a BV7 MKIII with Beolab 9s. All audio sounded much better.
Beovision 7-55 with Beolab 7-4, 9s and 4000s
Beovision 10-40 with Beolab 1s and 6000s
Beosound 1, 5, 2000, and 3000
Beotime, Beotalk, Beocoms