Oh and I just did a No Mod vs. Kees Mod comparison. I had my left driver modded and my right one was free of mods. Also did have both modded and unmodded for each track.
Opening Statement:
Now I first did the comparison through my laptop using uncompressed WAV music files. No Amp, DAC, or fancy cables, NADA! The sound was honestly the same, but that is because without an amp or DAC the Pro 900 sounds weak and muddy. Now when I pluged it into my rig, the sound change became more obvious. The Kees Mod essentially does what the Pro 2900 does only with a closed back. The mids are moved forward ahead of the bass and I sense a slight (but noticable) increase on the treble. I also noticed the instrument seperation and imaging were also improved. The Bass did take a heavy hit from the Kees mod, but not in a bad way (depending on how you like it). The bass is now tighter and punchy, but it doesn't have that slam and vibration the Pro 900 are known for.
From Here on end I will refer to the mods as "Kees Mod" and "No Mod", let us begin.
Track - Genre:
1. Benny Benassi - Cinema (feat. Gary Go) (Skrillex Remix) - Dubstep
On this track I actually perfered it using the Kees Mod. Now I know it reduced the bass (for Dubstep its MADNESS), but since there's so many sounds going on at once it made it more clean and sepertated all the sounds. The No Mod just sound like a mess and everything blended poorly.
2. Afrojack - Take Over Control (feat. Eva Simons) - Electronic/Dance
The Kees Mod won me over here aswell. Eva Simons voice lacked the passion and clarity on the No Mod. I did feel the track needed bit more bass on the Kees Mod, but Eva's voice just made me forget that.
3. Kanye West - Power - Hip-Hop/Rap
The No Mod was the winner in the Hip-Hop department. I felt Kanye's voice was moved a few spaces back on the Kees Mod. It also lacked the bass quantity which made the song sound weak and boring.
4. Lady Gaga - Born This Way - Pop
I felt it had the same effect as it did on the Kanye track. So No Mod wins.
5. Phil Collins - Another Day In Paradise - Pop/Rock
I really like the Kees Mod on this track. It brought out intruments in the background that were clouded by the bass on the drum before. It also moved Phil's voice slightly more forward which made me appriciate the song more as it gave me more of an intimate feeling.
6. Coldplay - Speed of Sound - Pop/Rock
It sounded like magic on the Kees Mod. The better speration of instruments made the felling that the soundstage was wider, while keeping the lead singer's voice right in the center of the stage. I actually listened to the whole X&Y album later on, great stuff.
7. Rob Zombie - Superbeast - Industrial/Metal
Rock is where the Kees Mod really shined for me. It made the guitars sound much more cleaner and moved them a bit forward and instrument sepertation was amazing. But I do listen to a lot of metal tracks, so I do miss the slam I get from the double bass drums. I honestly can't tell which I like more when listening to rock on the Pro 900.
Conclution:
The Kees Mod is great if your looking for more of a studio refrerence/analytical headphone and slightly more natural sound. Though if you are a basshead and can't get enough of it, I wouldn't recommend doing the Kees mod. But if you find the bass overbaring on the Pro 900, the Kees Mod might be your one way ticket to audio nirvana.
I will continue to edit this post if needed and if you'd like me to give an opinion/review on a specific song using (and not using) the Kees Mod feel free to let me know.