Q4Max adds many features and fixes to Quake 4, making it a much more enjoyable and complete game. For this reason, most servers running Quake 4 are running Q4Max.
In team games, the "multipov" feature allows you to follow all players of a team at once - there are several different layouts available to chose from - in this screenshot they all are the same size, but you may prefer to have one player focused and the other players smaller down the side, or along the top.
Notice how one player has the full hud drawn - this is the player for which the sounds are played.