Seeking Advice to Improve My Audio System ($1000 Budget)

Hello everyone. I have started collecting physical media (mainly Classical Music, but also some Metal, and older singer/songwriter material) for a few years now, and have built up a collection that is mainly vinyl, but also some CDs. I have slowly built up a stereo system to support it. I am not very knowledgeable with audio equipment and feel like I am drowning in information, and so I have pieced together what there seems to be a consensus around with my budget. So far I have:

Audio Engine A5+ 150 W Speakers

REGA Planar Plus 1 Turntable with built in stage

SMSL PL200 CD Player 

I use the RCA port for my turntable, and the aux port for my CD player.

Now I am wondering where I should go with my setup. I want my next investment to be around the $1000 range, but am not sure where to go with it. Should I get a woofer for the speakers and an external preamp for my turntable? Or at this price, am I better off looking for better speakers...or is there another weak point in my system? My main concerns are that the midrange and upper frequencies do sound muddy compared to other systems I have heard (but they aren't terrible) and while the bass isn't bad, it certainly could be enhanced.

As a final question, I am confused when it comes to the pre-amp. I don't quite understand how they work, and I am a bit confused and worried that I would run into an issue with my existing built-in preamp overriding an external one? Any advice?