SEEKING ADVICE: Which component would you upgrade first?

This is my first post, so take it easy on me!

I have a modest analog system and would like to get recommendations on which component you would upgrade first for the biggest impact. Please use the existing components as a gauge for my budget (+/- a few hundo).

About me: I'm music lover. I'm a musician and recording engineer. I have a decent collection of old and new records, CDs, and tapes, which I listen to regularly. I appreciate good sounding recordings and have the experience to identify good and bad, but I'm not interested in mortgaging my home to upgrade my system.

THE RIG

Receiver: Pioneer SX-680

Turntable: Pioneer PL-112D

Speakers: Yamaha NS-1 and Pioneer HPM-100