First iPhone 5S sound was not as crisp or loud enough for me, sent it back, got another and turned off Noise Cancelation, than I went into Setting > General > Accessibility >Mono Audio and turned it off. My sound is normal to me, and I have some old age hearing issues. May want to try this. Hope it works
Also noticed that when using SIRI, the sound is very low. While using SIRI, use the buttons on the left of the iPhone to boost the sound level.
I now use the Apple ear head phones, and the conversations are very clear at both ends. I have some Bluetooth headset (Plantronics arriving today) and will try those out as well.
Edited: Found this regarding EQ question..
"Note: EQ settings affect all sound output, including the headset jack and AirPlay. (EQ settings generally apply only to music played from the Music app.)"