Speaker Damage/Amp Power/Volume

I believe the upper bass driver on one of my Energy Veritas 2.3i speakers is damaged, as it has started to make a humming/vibrating/distorted sound on certain Lee Ritenour jazz guitar tracks. What is confusing is that I do not hear the vibration on most of the other music in my diverse collection of rock, jazz, female vocals and classical. I drive the Energy's with a Musical Fidelity A5 Integrated rated at 250w into 8 ohms and 400w into 4 ohms. While I never go past the "11:00" position on the volume dial, I have no idea how many db that represents or how many db is required to damage a speaker. My room is 16x30x9. How loud can you go? Energy recommends 50-250w for the 2.3i, not unlike the input suggestions for most of the speakers I browse. How are mega-watt amplifiers of up to 1000 watts paired with speakers whose specs call for up to 200 or 300? What speakers in the 3-4k used range are able to play louder with less risk of damage? I also wonder why more higher end amps don't possess a warning light like my second system Adcom 545 II--I think it says 'thermal protection'--and why speakers don't have built in protection. A bunch of Q's, I know, but I am newer to this great hobby and I'd like some A's before I upgrade my speakers. Thanks.