Speakers would be the biggest bang for your buck improvement IF you can afford 1500-3k on new speakers. I am personally a huge fan of Tekton Design Impact Monitors and Double Impact, but any of their designs with the seven tweeter array I'm sure is solid. Expect to wait weeks though and have trouble getting through to them at times. Although, they have some models available for sale right now on their specials section.
Otherwise KEF makes solid stuff if you don't like playing loud as I think their low end gets heavily distorted at higher volume typically at lower price points.
But yes, without knowing your budget, it's hard to give you advice. Speakers are by far going to give you the biggest change in your system though. But I'd say you'd have to spend $1500+ to get more than an incremental change. I'd go as far to say that with some $2000+ speakers such as the tektons, it would absolutely change your system into a different animal.
Wish you the best of luck in your system journey!