"I am there" vs. "They are here"

Hi,
all of us in this hobby have heard the exclamation "I'm there" or "they are here!" a counless number of times. Usually these remarks are issued forth when one's audio system has made a sonic leap in the direction of naturalism.
However, "I'm there" and "they are here" are clearly two very different remarks.

Would anyone care to describe in detail what about the sound of a great audio system that inspires the listener to make one remark rather than the other.

Which one is a higher compliment?

Thank you,

David