Subwoofer advice sought


I have a pair of Totem Forest Signature driven by a 100 wpc Unison Research Due amplifier. It has loads of power to power these speakers and has a subwoofer output. I have a medium sized room.

My local hi fi dealer said I would get better sound with the addition of a subwoofer with the results being better midrange and sound staging as well as better bass.  How is this possible?

The 2 subwoofers I am looking at are the Totem Storm and The REL T/7i. My dealer sells the REL and says it  would be a good match for the Totem speakers as it is very quick and tuneful.  Can anyone explain why a subwoofer would make these differences to the sound?  I also would be interested to hear from anyone with experience with these specific subwoofers or pairing a subwoofer with Totem Forests. Thanks.
traceyc
I don't often see 4-6 double bass players scattered throughout the venue to immerse you in their bass.
If you've ever been to a rock concert or especially an EDM show, the bass travels throughout the venue and you feel it as much as hear it.  That's one of the great things about having multiple subs is that it feels like live music.  I don't recall ever hearing the bass only coming from the direction of the stage at a live concert.  Of course it's been a while since I've been to a show, perhaps my memory is playing tricks on me.

@big_greg  You're exactly right...the bass is traveling throughout the venue even if it's originating from one side of the stage.  This is the effect of the venue or the room.  What you are experiencing is the room effect on bass.  They aren't creating it at the concert by putting bass signals in an array throughout.  You have a room as well that you listen to music within.  Look, I totally understand why a DBA would work and help counter the effects of uneven bass distribution in your room.  My point is that this technique is dealing with room acoustics and the whole point isn't to place the listener inside or "enveloped" within the soundstage. But like everything else, just pick what you enjoy listening to most and the way you enjoy it implemented most.  There is no wrong way.  
@three_easy_payments We're in total agreement that there's more than one way to get good bass and that different people will enjoy different things.  I've enjoyed good bass in my system with no subwoofers.  I have three other systems that all have one subwoofer.  One of the best systems I've heard had two subwoofers.

Using four subwoofers, I don't feel like the bass is enveloping in a surround sound way.  The soundstage is still very well defined, perhaps even better defined.  The performers are there in front of me, including the bass player.  If I'm listening to Yes for example, I can tell exactly where Chris Squire's bass is coming from.  It's not in surround sound, it's coming from a specific spot on the stage in front of me.  The sound fills my room though in a way that is the closest thing I've felt to live music in my system.  And yes, I enjoy it very much.

I'm not sure my words are adequate to describe the distinction between the surround type "3-D" listening experience you seem to think is created and what I experience.  Have you experienced a system with multiple subwoofers? 
@big_greg  I have not heard a DBA system and I was really commenting on the first response to the post stating:

Low bass improves the sense of envelopement, feeling like you are in the soundstage instead of it being just in front of you.

I think DBA is probably a good way to combat room nodes and help distribute bass evenly.  Good to hear it doesn't envelope you and place you inside the sound stage which would be an unnatural presentation in my view. I would like to check it out sometime, although it would been completely impractical to integrate into my mainly listening space which isn't dedicated to listening - it's my living room.  Life's a balancing act of priorities ;-)
@three_easy_payments If you're ever in the area and we don't have to worry about killing each other by sitting in the same room I'd be happy to let you listen. My system is in my living room. It's not ideal, but it works.