Some generic recommendations. I usually use 1/12th octave smoothing before running eq filter design in REW. The generated filters don’t look too bad though. With smoothing you are also less likely to end up with high-Q eq filters that usually sound bad.
Note that if you allow +9 dB boost, you need to check the max boost generated for the filters and set gain compensation in HQPlayer accordingly. That will drop the overall level for example by 9 dB, but avoids running to peak limiting when music content happens to contain frequency that hits the boost peak…
Another recommendation is to keep corrections only up to 1 kHz or lower, usually problems are in the bass range. However, do not try to fill up null points with excessive max boost (I’d recommend 6 dB max boost), that won’t be possible but attempting it will have adverse effects.
Coming up with good target curve is essential. Good starting point is straight line from 20 Hz to 20 kHz with about -6 dB drop at 20 kHz vs 20 Hz. One of the commonly referred and popular ones is the B&K house curve:
