Will a subwoofer add depth and clarity to my system, or just bass?

hi folks,
I just purchased a set of Focal Aria 906 speakers with stand, powered by a Bluestream PowerNode (not my ideal system but I had a limited budget).  I think it sounds really good, but am wondering if an upgrade to a subwoofer is worth it, and if so, what would pair well with this system -- my audio guy recommended the JL Audio D110 10" Dominion Subwoofer, but that's out of my price range.  Perhaps a SVSPB1000, for $499?  My room isn't very big, and I don't use the system for movies, just listening to mostly jazz and rock (and classical).
Thank you!
Dear @noble100  : """  Two subs can provide smoother bass response at the listening position but the bass will be mono..... """

Why " will be mono " ?, I can't understand that. Coud you explain about?

Thank's in advance.

Hello rauliruegas,

     The bass will be mono because there's no such thing as true stereo bass below about 80 Hz and there are virtually no vinyl or cd recordings that have separate bass recorded for the L/R channels.  The recording engineers sum the bass below a certain frequency and evenly distribute the combined bass on the L/R channels so it is located to the center when played back via a stereo system through a pair of speakers.

     In my opinion the best sounding solution, if you're going to use 1 or more subs, is to run them in mono mode and position them at positions in the room that sounds the best to you (smoothest and most natural) at the listening position.  

     The major benefit of this approach is that the deep bass will be perceived as stereo (even though it's not recorded in stereo) from your listening position.  This is a result of the higher frequency harmonics or overtones of the fundamental deep bass tone being recorded and played back through the L/R stereo speakers since they generally extend above the approximately 80 Hz frequency that the bass is typically summed in the L/R channels in mono.  
     These higher frequency harmonics/overtones give clues to our brains.  Our amazing brains are able to process the non-directional inputted deep bass fundamental tones, along with the directional higher frequency harmonics/overtones or clues,  determine  that they are related and assign a specific room location the non-directional deep bass tone originated from.

     This is generally referred to as a psycho acoustic effect but it is consistently perceived as sounding very real to us humans.

Hello noble100,
    Just a quick note - I am Jim Smith, author of of Get Better Sound, the Quarter Notes newsletters, and the "Subwoofery" series of seven articles on subwoofers in Copper e-mag.

    I rarely post here, but thought a few points might be helpful in this instance:
    You mentioned that you read the book twenty years ago.  Actually, it was introduced in late 2008, and began shipping in 2009 - a bit over 10 years ago.
    I know Duke and have communicated with James. IMO, they are both men of integrity. I do disagree with some of what they espouse, as they probably disagree with me.  Even so, what they suggest is w-a-a-a-a-a-y better than what most folks hear or know about the need for subs and how to set them up.
    FWIW - Audiogon shows that I signed up in 2014.  It was actually in early 2001, IIRC.  I was the North American distributor for Avantgarde Acoustics from 1999 through 2005. Hence the Hornguys username. 

    Carry on!  Don't want to take this thread off track.

@hornguys I was really surprised to see your post - from the author himself! I mention this because I ordered your book (& DVDs) just 2 days ago after having read many good things about it on several sites/forums including AG.

I must admit I was a bit concerned when I read @noble100 's comments that seemed to indicate the book was perhaps outdated. However, I do feel better now after seeing your response :-) 

I'm looking forward to the book for advice and help on improving my setup at home, any further tips are most welcome!
Dear @noble100  : The information in the recording R2R  ( part of the overall recording proccess. ) comes in stereo way including bass range and is only when starts the LP cutting procces when the low bass range is switched to mono due the severe limitations in the LP analog alternative.

Cd's comes with low bass signal in stereo not mixed mono.

You speaks on bass frequencies to 80hz but over 50hz ( or lower ) the signal in the LP comes stereo not in mono fashion.

My take is that we have to wired the subs in stereo way. The high pass filter in that 4 subs array has a very gentle filter that permits that perhaps from 150hz-200hz those subs are reproducing " sounds " if are wired mono then not only affects the fundamental notes but its harmonics and things are that the bass range ( notes/harmonics ) are the main frequency range that tames the overall  frequency reange we are listening through each one of us room/audio system.

Sure I can be wrong about but with the information I have that's my take: subs wired stereo.