It all really depends on what kind of stuff youre running.
If you run 2 6.5s and 8 tweeters, its going to sound horrible. If you run 16 6.5s and 2 tweeters, its going to sound just as bad. If you run nice tweeters with crappy mids, its going to sound bad. Etc, etc.
The reason why so many BIG pro audio setups sound bad is because they are so hard to get right.
When youre running 4 6.5" comp sets in a car you set the gain, then play with settings for a few minutes and it sounds great.
In a car with 30+ mids/highs on 4+ amplifiers, settings the amps and EQing it to sound right is a nightmare. Its doable, but it takes FOREVER.