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!
jazz99
Yes a very good quality sub at least in the $1k andup club 
will give great precision in the Bass and bass fundamentals 
up tothe midrange  which for sure adds depth and coherence to the musical performance.
hi folks,
Many thanks to all of you for your advice and recommendations.  I have a lot to learn about optimizing music and sound in general.

I'm just back into good audio after earlier stints with Vandersteen speakers and Grado RS-1 phones, but with a limited budget.  So all of this information is really helpful.  I suppose one rule to follow is... audition a piece of equipment and if it doesn't do it then return it (easier with a store nearby).  Given my small budget I may start with the SVS SB1000 and perhaps try the 2000 if that becomes possible.  My understanding is that the SVS line is the best at this price point (under $1000).  

Tim, thank you for your detailed information about setting up the system. hat will take some time, but it appears to be time well spent in really getting the right balance.  It helped a lot.

I really like how the speakers sound, and the PowerNode II with Bluos app running Tidal CD quality tracks is easy to use.  But this set of comments reinforces the idea that a sub is the way to go to make the system really sing.
thank you!
paul
Look into Rythmik subs. Powered, servo controlled, with a good set of adjustments available, not very expensive. I made heavy sealed boxes for a couple of their 12" kit. They also sell finished subs. Also look into their double 8" subs, also servo controlled. These have the advantage of being able to play higher (to 150Hz, easily) which could be an advantage with standmounts. 
Yes, a sub makes a positive difference. Best to check it out in your own home to see if it’s worth the money. Read into the MartinLogan Dynamo 800x. It’s a bit more than $500. Features Anthem room correction and tons of other settings. This way from your app you can blend the sub and fine tune every setting. This is a good situation if you are running a 2 channel rig without room correction. It’s a compact sealed design. Super fast and punchy. Many online retailers offer generous exchange policy. Ultimately the in home trial is the only way to be sure. Good luck and great question.
I am convinced that adding a pair of subs 
1. Improves the bass range
2. Cleans up the midrange 
3. Widens the sound stage .
the key being placement and tuning ie the phase setting and volume of subs.
i use my pair of kef blade 2s along with a pair of Jl Audio f113 v2. The sound improvements after adding the subs were phenomenal through the entire spectrum.
i am not a profound supporter of room sound correction programs .
noble100 was right on the dot till recommendations no 5, from that point on I tend to differ from him. Not saying he is wrong but saying his techniques are different .
i would recommend you contact Barry Oder ie the sound doctor. His experience with subs spans over 4 decades. I spent a weekend with him and learnt a lot which I have used for setting up my sound . If you call Jl Audio for help they would guide you to the white papers written by Barry . He is a true guru .
http://www.soundoctor.com/whitepapers/subs.htm
Read the above paper written by him and you can contact him over phone . He is a tremendous resource and loves to help people who love bass. Who doesn’t . 
You don’t need a Jl Audio sub to make great music but you need to have it perfectly aligned with your main speakers to sound great .time domain is in my opinion crucial .