Next upgrade to an entry-level system?

I would follow the advice @tablejockey has provided. New transducers will not be a great improvement and the 301 is a good integrated but has limitations. New transducers will probably bring this into sharp focus.  The RP-500s are a fun little speaker and are a good match for the 301. My son had a similar setup in college and it sounded great in his apartment. 

@tablejockey -

Good call with the outboard phono preamp. The 120 is a good TT.

If the OP has an extra two bills to throw at this, I might also go for an Ortofon Blue or Goldring E3

https://www.whathifi.com/ortofon/2m-blue-mm/review

https://www.whathifi.com/goldring/e3/review

Rich 

@parkergetdean 

+1

Typically the best way to upgrade your system is speakers first. Then bring all of your other components up to that level to get the most out of those speakers. You cannot shop by price, you must shop through professional reviews and listening to each component, but ultimately it is often true that through diligent work you will end up with components around the same price since they re similarly constrained by subcomponent and manufacturing costs. 

For speakers you want to take you time, audition many until a set tugs on you emotionally. You want emotional connection. You should also stretch as far as you can financially since this is the core component and effects everything you hear. From there on you want to get the best possible electrons to support the speakers. Assuming your components are analog then think 30% for speakers, 17% amp, 17% preamp, 17% phonostage, and 17% turntable... OK that is only 98%... it gets the point across.

I would add another subwoofer and then as mentioned the phono stage.