Subwoofer or Bi-Amp?

Bi Amping will improve the sound of your system within its present frequency range but, unless you are using a grossly inadequate amp, will not increase the frequency range of the speaker. It may better utilize that range, but to extend the range downward you need a dedicated subwoofer. That in where the name comes from. A good sub will add to the bass range of your system and produce a greater sense of realism whether or not very low bass is present. I use REL, HSU,and NELSON REED but there are many good ones.

Yes biamping with a powered sub will be a great improvement. I know from experience. However be prepared to also purchase an active crossover like a Marchand or Bryston or maybe even one of the digital room correction pieces with a built in crossover to analyze your room. Then, unless you can afford to pay someone who really knows the ins and outs of subwoofer/crossover setup be prepared for lots of tweaking which will include subwoofer placement, finding the modes and dips in your room's frequency response, dialing in the proper crossover points and slope, and of course proper placement of your listening position and main speaker position. You can do all this yourself but it may take many hours of frustration. In the end though, the sound of your room/system will improve astonomically. Also be prepared for the added expense of interconnects that will match the level of your current systems needs.
Before you start this project make sure you've got proper bass trapping through out your room as nothing you do above will make as profound a difference as this.

I have gained this knowledge through my own experiences.

As to your other questions, yes vertically biamping will help and you'll here a significant difference. However it will not transform your main speakers into separate subs and mid/high frequency speakers. I've done this, (and still do) but the addition of subs powered with their own amps is the better way to go, if your goal is to transform your system from great, to something that you can really be proud to own.

I'd be glad to share further insights in depth if you'd like. Talking is easier than typing.

Hope this helps,
Steve

Stan said it. Improvement? Yes.

sufficient enough to dispell the need for better bass?

That's entirely your call... doubtless IMO standard speakers can outrun an active dedicated sub though, as not too many speakers reach far below 30Hz without roll off, or near the impact a sub would provide.

Size of, or tuype of, sub? The room, present speakerage, and your preffs should make that call.

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.

Hello again and thanks for all the replies. I also thought it might be of some help to inform everyone that my application would be a two channel music only system. Thanks again. All of the responses have been enlightening.

Darkkeys,

The lowest note on a bass guitar is an E, which resonates at 42 (actually 41.20) Hz, which is why you were able to hear it clearly, but not the subwoofer.