the cart or the horse?

I currently own a Parasound ZAMP, Denon PRA-1500 preamp, and Omega 7's speakers. I stream through a Bluesound Node 2i.  All this resides in a home office of approx 15x10. 

I am not happy with the sound and do not know which component to attack first. There is a lack of presence and body and the sound is well.......boring. I listen to jazz at low volumes and would like your opinion on what to work on first. 

Replace amp,preamp, or speakers? The cart or the horse? My budget is very modest but am willing to go step by step. 

All my best,

Andy