[Xiaomi Redmi Note 3 Themes, Apps, and Mods] chdloc:
Please allow me to add a few comments:

It should be possible to use biQuads to compensate the speakers asymmetrically. This post details the steps necessary for the Nexus 5, which you can use to adapt for your device.

The modified mixer_paths file that you posted for your device probably does not work for biQuads as intended. Replace your "headphones" section with this:

<path name="headphones-chdloc">
<!-- setup the codec -->
<ctl name="SLIM RX0 MUX" value="AIF_MIX1_PB"/>
<ctl name="SLIM RX1 MUX" value="AIF_MIX1_PB"/>
<ctl name="SLIM_0_RX Channels" value="Two"/>
<ctl name="IIR0 INP0 MUX" value="RX0"/>
<ctl name="IIR1 INP0 MUX" value="RX1"/>
<!--
IIR filter cofficients and biquad enable
-->
<!-- all biquads set to passthrough mode -->
<ctl name="IIR0 Band1" id="0" value="268435456"/>
<ctl name="IIR0 Band1" id="1" value="0"/>
<ctl name="IIR0 Band1" id="2" value="0"/>
<ctl name="IIR0 Band1" id="3" value="0"/>
<ctl name="IIR0 Band1" id="4" value="0"/>
<ctl name="IIR1 Band1" id="0" value="268435456"/>
<ctl name="IIR1 Band1" id="1" value="0"/>
<ctl name="IIR1 Band1" id="2" value="0"/>
<ctl name="IIR1 Band1" id="3" value="0"/>
<ctl name="IIR1 Band1" id="4" value="0"/>
<ctl name="IIR0 Band2" id="0" value="268435456"/>
<ctl name="IIR0 Band2" id="1" value="0"/>
<ctl name="IIR0 Band2" id="2" value="0"/>
<ctl name="IIR0 Band2" id="3" value="0"/>
<ctl name="IIR0 Band2" id="4" value="0"/>
<ctl name="IIR1 Band2" id="0" value="268435456"/>
<ctl name="IIR1 Band2" id="1" value="0"/>
<ctl name="IIR1 Band2" id="2" value="0"/>
<ctl name="IIR1 Band2" id="3" value="0"/>
<ctl name="IIR1 Band2" id="4" value="0"/>
<ctl name="IIR0 Band3" id="0" value="268435456"/>
<ctl name="IIR0 Band3" id="1" value="0"/>
<ctl name="IIR0 Band3" id="2" value="0"/>
<ctl name="IIR0 Band3" id="3" value="0"/>
<ctl name="IIR0 Band3" id="4" value="0"/>
<ctl name="IIR1 Band3" id="0" value="268435456"/>
<ctl name="IIR1 Band3" id="1" value="0"/>
<ctl name="IIR1 Band3" id="2" value="0"/>
<ctl name="IIR1 Band3" id="3" value="0"/>
<ctl name="IIR1 Band3" id="4" value="0"/>
<ctl name="IIR0 Band4" id="0" value="268435456"/>
<ctl name="IIR0 Band4" id="1" value="0"/>
<ctl name="IIR0 Band4" id="2" value="0"/>
<ctl name="IIR0 Band4" id="3" value="0"/>
<ctl name="IIR0 Band4" id="4" value="0"/>
<ctl name="IIR1 Band4" id="0" value="268435456"/>
<ctl name="IIR1 Band4" id="1" value="0"/>
<ctl name="IIR1 Band4" id="2" value="0"/>
<ctl name="IIR1 Band4" id="3" value="0"/>
<ctl name="IIR1 Band4" id="4" value="0"/>
<ctl name="IIR0 Band5" id="0" value="268435456"/>
<ctl name="IIR0 Band5" id="1" value="0"/>
<ctl name="IIR0 Band5" id="2" value="0"/>
<ctl name="IIR0 Band5" id="3" value="0"/>
<ctl name="IIR0 Band5" id="4" value="0"/>
<ctl name="IIR1 Band5" id="0" value="268435456"/>
<ctl name="IIR1 Band5" id="1" value="0"/>
<ctl name="IIR1 Band5" id="2" value="0"/>
<ctl name="IIR1 Band5" id="3" value="0"/>
<ctl name="IIR1 Band5" id="4" value="0"/>
<ctl name="IIR0 Enable Band1" value="1"/>
<ctl name="IIR0 Enable Band2" value="1"/>
<ctl name="IIR0 Enable Band3" value="1"/>
<ctl name="IIR0 Enable Band4" value="1"/>
<ctl name="IIR0 Enable Band5" value="1"/>
<ctl name="IIR1 Enable Band1" value="1"/>
<ctl name="IIR1 Enable Band2" value="1"/>
<ctl name="IIR1 Enable Band3" value="1"/>
<ctl name="IIR1 Enable Band4" value="1"/>
<ctl name="IIR1 Enable Band5" value="1"/>
<ctl name="RX INT1 DEM MUX" value="CLSH_DSM_OUT"/>
<ctl name="RX INT2 DEM MUX" value="CLSH_DSM_OUT"/>
<ctl name="RX INT1_2 MUX" value="ZERO"/>
<ctl name="RX INT2_2 MUX" value="ZERO"/>
<ctl name="RX INT1_1 MIX1 INP0" value="IIR0"/>
<ctl name="RX INT2_1 MIX1 INP0" value="IIR1"/>
<ctl name="RX HPH Mode" value="CLS_H_HIFI"/>
<ctl name="COMP1 Switch" value="0"/>
<ctl name="COMP2 Switch" value="0"/>
</path>

<path name="headphones">
<path name="headphones-chdloc"/>
<ctl name="IIR0 INP0 Volume" value="84"/>
<ctl name="IIR1 INP0 Volume" value="84"/>
<ctl name="RX0 Digital Volume" value="84"/>
<ctl name="RX1 Digital Volume" value="84"/>
<ctl name="HPHL Volume" value="13"/>
<ctl name="HPHR Volume" value="13"/>
</path>

In addition, to avoid issues with hotword detection, you will also need to remove all plumbing for sidetone in your mixer, i.e. all references to "<ctl name="IIR0 INP0 MUX" value="DECX" />" in the adcY devices. (Y=1,2,3,5,6)

Use this one for a systemless root installation. The one in my OP is at this time outdated.

A couple of general comments:

Don't increase gains past 84 (which corresponds to 0 dB) or you will introduce distortions. If you really want to increase headphone gain, raise the "HPHL/R Volume" values in the mixer (max value is 20). Each "tick" corresponds to 1.5 dB. You used 13, so you have 10.5 dB more headroom. However, please increase headphone playback levels responsibly.

The "high performance" DAC settings have absolutely no measurable effects on wcd9320 (e.g. Nexus 5), wcd9330 (e.g. Note 4), and wcd9335 (e.g. Pixel) based devices. I have not seen (or measured myself) any other devices, but I really don't think they will make any difference there, either.