I don't have sibilance problems, are my speakers dull?

Hello,
I get it when listening to Diana Krall. As long as it doesn’t hurt my ears it doesn’t bother me. It may be a preamp issue. You could try changing you power cable on your preamps to a thicker gauge. It really makes a difference. The Puritan Classic Plus power cable is a cheep fix for this. 

Sometimes sibilance is just baked into the recording.

I think we all have that subconscious (or conscious) "Do Not Play" list.

Who can say for sure?

Sibilance to me is very different than the sound I've very rarely heard when DACs just don't seem to like a particular recording.  There was a song by Halie Loren (now I can't remember) which I owned and on one DAC it would consistently distort, more like paper being crumpled.  Switch DACs, problem went away.

I used to have bouts of sibilance with various recordings (Linda Ronstadt's "What's New" for sure) on Martin Logan SL3s and on Dynaudio Sapphires with the Esotar 2 tweeter.

I feel I have no sibilance ever anymore on pretty much any recording I own since moving to Raidho D2s (sealed ribbon tweeter).  What is even better is that the D2's far superior resolution is simply stunning and they have opened up every recording I own over the other speakers. The greatest tweeter ever for me (and mid-woofers).