Yes, that is the way to go in this case--use a crossover to a tweeter or a line of tweeters. I've found that simple first order crossovers (single component) aren't sharp enough for most line array implementations so a third or fourth order usually works better. Furthermore, the crossover likely will need to be when the midrange line starts to lose sensitivity. This would likely be in the 2-3.5 kHz area. Measurements help to determine specific crossover points.

Jim