Going from CS5i’s to stand mounts with tubes could be a very different contrast.
B&W’s usually aren’t very compatible with tubes. Just look at Fig. 1 for the 805’s
B&W Matrix 805 loudspeaker Measurements | Stereophile.com
That rollercoaster frequency response is not what tubes typically like to see.
Personally, I don’t much care for the B&W sound, though I once heard a pair of 802’s in a very unusual room powered by ss/tube hybrid Counterpoint amp making some beautiful work of a chorale performance. The demonstrator shut down the system after about 20 minutes, because he was afraid the amp might go up in flames.