Upgrading sub to get a live feel.

I currently have a set of JBL 4319 which has its history as 4310. They are studio monitors and as a result they sound like studio monitors you hear everything, but they lack the physical presence on the low end. They have wonderful mid range and voice presence. I also have a pair of SVS SB1000 to help with the low end. 

I want to eventually upgrade to JBL 4367 with upgraded pair of subs, for this reason, but in the mean time would a sub upgrade be considered before the speakers. 

You Might try the Sub upgrade now..Many good ones out there.You could move up the SVS food chain and still be quite usable with your current JBL's.Those JBL 4367 are $15,000 correct?
My current short list of subwoofers are

JL F113 or Seaton Submersive

Most likely Seaton

I am hopping that the sub upgrade will hold off my 4367 purchase. 

     You may be able to improve the bass response at your listening seat just by repositioning them.  I'd suggest using the crawl positioning method sequentially for each.
     If this doesn't work and you have the room space, using three SVS-SB1000s, sequentially positioned using the crawl method, is virtually guaranteed to provide bass response at your listening seat approaching state of the art.  This is called a distributed bass array (DBA) system and it works amazingly well in virtually any room and with any pair of main speakers, even with faster and very detailed speakers like electrostatics and Magepans.
      The bass perceived is very smooth, detailed, as powerful and dynamic as the music requires, seamless integration with any pair of main speakers and an overall quality of effortless bass on music and HT.
      I use a 4-sub DBA system called the AudioKinesis Swarm in my 23'x16' room with large Magnepan panel speakers and it works like a charm.  The DBA concept usually requires four subs to function properly but works almost as well with three.  
     Here's an Absolute Sound review of the AK Swarm that gives a good explanation of how it works and what to expect.  The SB-1000 subs are ideal to use in custom DBA systems because they're very good subs and are relatively small.