Hi asher770,
"Sibilance"--exaggerated "sss" and "ttt" sound--is often heard on FM broadcasts, the result of microphones that have a peaked "presence" effect in the upper midrange, for intelligibility of the announcer's voice heard on lower-fidelity gear (car systems, tiny radios, boomboxes, etc.). The upper-midrange peak is inherent in the microphone design, or sometimes added with a touch of EQ by the radio station engineer. Linear speakers like the M80s, M60s, etc. will reveal sibilance in the source material, whether it's FM or CDs.
You would never hear it on AR speakers, which historically have had very depressed upper midrange and treble. In tests of AR speakers, including models I owned (AR3s, AR2ax's), the treble and upper octave response was down by 10 dB! That's equivalent to turning a treble tone control fully down (counter clockwise).
Many pop and rock recordings (some classical and jazz) are also EQ'd in the mids (again for radio airplay), so they may be sibilant played on linear speakers. As an example of this, I once spoke to a Canadian jazz singer, Holly Cole, about the microphone she used for live performances (and a similar one for some of her recordings). It had a pronounced midrange presence peak that made her concerts really irritating, with sss and tt sounds that could take your ears off. At a Toronto reception after a concert, I politely mentioned the subject, and she seemed to appreciate my comments. Whether she changed mikes for later concerts I don't know. Some of her later CDs do not have the sibilance that earlier discs had, so perhaps my remarks influenced her.
Anyway, use your tone controls to tame annoying FM broadcasts or CDs that have excessive inherent siblilance. Often a 2-or 3-dB reduction in the treble will make it quite listenable.
As to "depth," lots of rock or pop recordings don't have any. They are entirely artificial studio creations so you will get a flat soundstage. They are multi-miked and digital reverberance is sometimes added to make them a little less dry-sounding.
On the other hand, if you play some recordings that are simply miked (concert classical or jazz done in a live venue), the M80s should reproduce that sense of depth quite realistically.
Regars,
