I have been searching for some tips on how to properly equalize my Klipsch Reference S4 inner earbuds. I had my Rockbox EQ tweaked for my Ultimate Ears, but since those broke I really needed to get my EQ settings for the S4s.
This was complicated by the fact that I really didn't know much about a parametric equalizer, so the Rockbox Clip+ implementation is not terribly meaningful to a noob. So I came up with a method that allowed me to configure the EQ on my desktop and translate that to my Rockboxed Clip+. I know it's not exactly precise, but my method provided a "good enough" analogue so that I only needed to tweak the settings once I got the EQ onto the device.
Setup:
BE SURE TO DISABLE ALL SOUND CARD ENHANCEMENTS AND OTHER (WINAMP) EQUALIZERS

I loaded up my typical sample file, indicative of the music I listen to (heavy guitars, vocals and lots of loud / quiet variation),
"Quake" by Balance & Composure. I configured a 10 band EQ in Winamp / Electri-Q. I took the settings and translated them into Rockbox. Here are the settings for anyone interested.
EQ
# .cfg file created by rockbox 3.13 - http://www.rockbox.org
eq enabled: on
eq precut: 45
eq low shelf filter: 30, 20, 70
eq peak filter 1: 40, 12, 50
eq peak filter 2: 70, 10, 15
eq peak filter 3: 130, 7, -15
eq peak filter 4: 220, 7, -35
eq peak filter 5: 560, 28, -5
eq peak filter 6: 1010, 12, 10
eq peak filter 7: 2310, 20, 25
eq peak filter 8: 4690, 16, 50
eq high shelf filter: 8690, 13, 65
Additional Sound Settings
# .cfg file created by rockbox 3.13 - http://www.rockbox.org
volume: -21
balance: 0
bass: 1
treble: 2
channels: custom
stereo_width: 95
replaygain type: off
replaygain noclip: off
replaygain preamp: 0
crossfade: off
crossfade fade in delay: 0
crossfade fade out delay: 0
crossfade fade in duration: 2
crossfade fade out duration: 2
crossfade fade out mode: crossfade
crossfeed: meier
crossfeed direct gain: -10
crossfeed cross gain: -30
crossfeed hf attenuation: -60
crossfeed hf cutoff: 2000
dithering enabled: on
timestretch enabled: off
compressor threshold: -6
compressor makeup gain: auto
compressor ratio: 4:1
compressor knee: soft knee
compressor release time: 500
I've done a lot of searching and reading about equalizers, I hope this helps at least one other noob.