I pulled the DSP Manager app and library from the June 11th Cyanogenmod nightly build for the M8. I also pulled the audio_effects.conf file from this patch: http://review.cyanogenmod.org/#/c/65...o_effects.conf . I packaged the three files into a .zip that can be flashed from recovery (I've tested with TWRP). I tested this on my phone running stock 1.55.605.2 firmware.
I suggest backing up via nandroid or other means before flashing this. You're on your own if this breaks your phone, as I only know that this works on my phone and make no promises that it won't brick yours or burn down your house /etc.
I also suggest disabling "Boomsound" by editing the following line in /system/customize/ACC/default.xml to change the value for 'support_boomsound_effect' to 'false':
<item type="boolean" name="support_boomsound_effect">false</item>