What should I upgrade first on my budget system?

@coryb are there aspects of the system that you do not like? Or things that you feel it should better?

(that is where I would start.)

Usually a highpass filter to your amp/speakers… and adding a sub to fill in the bottom would often free up the amp and speakers.

but… that assumes your amp and speakers are over taxed with low notes, or that you want more SPL in the low registers.

So I am not sure there is a rational reason to upgrade without some goal or thing to improve… and maybe just going slow is best?

(And enjoy what it does for now)

 Start from scratch, asking for advice on an audio forum.

@carlsbad +1! Speakers offer the best-bang-for-the-buck! I can only recommend what I use: DCM Time Windows and Ohm Sound Cylinders. Two great classic designs that can be found at affordable prices. Both are competitive with today's four-figure speakers! 

The rest of the OP's system is fine! Depending upon how much he has invested in LP's a cartridge upgrade would be good. A Hana SL plus an SUT is an easy recommendation. Keep the PS Audio preamp and the Will Vincent Baldwin tube amp. Both units offer excellent sound quality! 

@ghdprentice : I think you are mistaken when you state that streamer sound quality is better than CD. You are at the mercy of whatever compression schemes the streaming services use to squeeze their data files to fit on the digital pipelines! No thanks! I will stick with my CD players/transports and extensive CD collection.