Just to be clear I have a 2016 Premium with an all stock stereo (non-navigation) and stock speakers. I was planning on upgrading the speakers, but now I might not. At least for a while
I saw a video where a WRX owner did this, and I thought I'd give it a shot... It definitely helped the stock stereo sound better than what I was able to do on my own playing around with the settings. The video is long and boring and I didn't agree with a couple things, so I thought I'd write a short post with the steps.
First off if you haven't already, then turn off these settings. Especially if you like to crank up the volume, because they just cause distortion at higher levels. If not, then it might not matter much.
Sound Restorer - Off
Volume Smoother - Off
Virtual Bass -Off
Then comes the really important part. Go to "Vocal Image Control" and move it all the way forward to 8 or 9. This moves most of treble to the tweeters, and frees up the door speakers for the mids and lows. I NEVER would have thought to do this, but it makes a huge difference.
Now you can go in and adjust your EQ settings the way you like it. Here's what I ended up doing. The bass is actually punchy and the highs are clear and bright without the mids overwhelming everything like it used to. It actually sounds pretty GOOD!
I also have an EQ setting with less bass for certain music, and one with even less bass that's more flat for talk radio.