Imaging is the placement of the performers and instruments on the stage. Really good systems can present a whole orchestra with great accuracy allowing you to guess how the different sections were placed. Related to imaging is the concept of soundstage. A performace in a 100 foot wide stage with a high ceiling should sound like that, not a small soundproof recording studio. Soundstage width is quite easy to recreate, soundstage height and depth tend to more complex.
Pace is the speed and rhythm of the system.
A system may sound slow and stodgy, unable to keep up with a fast bass line. Another system may be so lightning fast that transients begin and stop with atomic clock accuracy. A system with good pace accurately keeps up with the music's tempo. A bal anced set up Like all things in life, your hifi should be balanced. No, I'm not talking about balanced topology but a balanced presentation.