Any instrument including bass guitar produces much wider range than subwoofer can do. So without main speakers subwoofer alone will definitely sound dull.
In my opinion powered sub AND finely tuned crossover is better than bi-amping. Even better is to use two subs. But everything should be carefully tuned.
In my opinion powered sub AND finely tuned crossover is better than bi-amping. Even better is to use two subs. But everything should be carefully tuned.