Best Stereo Upgrade Value

Best upgrade?

Clean your ears. 

Speakers, considering the Dyanaudio Sapphires were substantially bettered in every single way but sheer dynamics when I moved to older used Raidho D2s.

BUT, my DSPeaker Anti-Mode 2.0 room correction unit with DSP took the D2s to a whole new level of superior sound quality in the room. It was just as amazing an improvement, and for the modest money, a far higher value for cost/performance.

Upgrade value depends upon your system.  In my modest secondary system (Yamaha AVR, NHT Super Zero Speakers, Pecan Pi Streamer) I recently replaced an old sub woofer with an SVS 3000 Micro sub.  I followed SVS guidelines and changed the subwoofer crossover to 120 Hz while getting the new sub dialed in.  The combination of the new sub and new crossover setting made a quantum improvement in sound for both two channel listening and for movies.

I think that the new sub woofer helped me to maximize the sound quality in this system. 

The singular, most significant item any of you can buy is a USB microphone and measurement program. It terms of sound quality everything else pales in comparison. Those of us who have experience with this die laughing when people say they can do this by ear.

Folks can argue forever but @jmijostyn is correct.

And a simple DSP room (and speaker) correction is one is the most incredible values out there. One should try it and A/B the sound without. It will take what you have to a higher lever. I will never go back.