Subwoofer or Bi-Amp?

I appreciate all of the responses so far. I had another subwoofer question as well. The sub I heard playing alone, with no other sat/full range speaker online sounded very muted and more resonant sounding as opposed to a very clear distinct sound of for example, a bass guitar. Is what I was hearing correct or was I listening to a defective suwoofer. However, the sound when the subwoofer was used with a pair of full range speakers was very coherant and full, etc. The sound with the subwoofer online had a lot more impact in the bass range along with creating a more life like presentation of the musical performance. Thanks again.

What you heard was correct. If the sound is clear then the crossover point is set way too high or it is not really a subwoofer. You are adding JUST the very low frequencies and should not "hear" the sub at all. I usually can't tell if mine are on when I am standing next to them but If I put my hand on them I can feel strong vibrations. The ear is not very sensitive to direction at very low frequencies. Your description was exactly what a good sub should do.

While I can't comment on bi-amping, the subwoofer made a big deal of difference in my system. I have 4 large speakers, so called fullrange, but because of positioning in my living room and without room treatment at all, I was getting an abysmal bass response. I doubled the amplification power but I got only minimal improvements. by adding a subwoofer the sound is now just as I like it, well balanced. I don't think be-amping would have accomplished that in my room. But every room is different.

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.

Sub for sure.