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I'm pretty sure I've got these perfect now. The bass is flat ala Stax/Etymotic and I've fixed the driver peaks, the BIG driver notch at around 4 kHz, and the ear canal resonance everyone experiences around 7.5 kHz.

The first eight filters, since a Rockboxed portable only allows 8 peak filters right now:

Filter 1: ON PK Fc 128 Hz Gain -3.3 dB Q 1.00
Filter 2: ON PK Fc 20.0 Hz Gain 10.0 dB Q 0.80
Filter 3: ON PK Fc 60.0 Hz Gain -2.0 dB Q 1.00
Filter 4: ON PK Fc 144.0 Hz Gain -1.0 dB Q 0.20
Filter 5: ON PK Fc 3,829 Hz Gain 6.0 dB Q 5.00
Filter 9: ON PK Fc 7,500 Hz Gain -7.0 dB Q 7.00
Filter 11: ON PK Fc 8,500 Hz Gain -4.5 dB Q 7.00
Filter 12: ON PK Fc 11,600 Hz Gain -4.0 dB Q 7.00

Set the precut/EQ preamp/media player preamp to -10 decibels to prevent clipping.

The one at 7,500 Hz (filter 9) you will need to use a sine wave generator such as Sinegen to locate the precise location of because the location will vary from listener to listener, as that's a major ear canal resonance. The other filters past 1,000 Hz may need slight adjustments to the center frequencies as well depending on your ears; again, use Sinegen for this.

Finally, four more little tweaks in case you're using an EQ that supports more than 8 peak bands:

Filter 6: ON PK Fc 1,968 Hz Gain -2.5 dB Q 8.00
Filter 7: ON PK Fc 4,600 Hz Gain -2.5 dB Q 10.00
Filter 8: ON PK Fc 5,400 Hz Gain 1.5 dB Q 10.00
Filter 10: ON PK Fc 7,000 Hz Gain -2.5 dB Q 10.00

If you're using an EQ with bandwidth instead of Q, there's Q/bandwidth converters online you can use. Rockbox can't get some of these values exact, but close enough.

These little babies sound amazing right out of the box with no EQ for $10 headphones (or for $100 headphones, for that matter), but with these EQ settings you're going to seriously question the need to ever spend tons of money on headphones.

I hope this helps out someone with these awesome budget cans. If anyone uses these settings, let me know how it sounds for you.