I have a problem, I don't hear much wrong with the stock T50RP.
Please bear in mind that my main (and so far favourite) headphone is AKG K501, known to have a lush midrange. Smooth, airy, and relaxed sounding. And not known to be a bassy headphone. I do not like headphones with energetic trebles, and in this categories are DT880, DT990, most of the Grados, and etc. I also do not like aggressive and fatiguing sound. I also dislike a smoothed over sound with no texture, and muffled sound (with certain material, I find Westone 3 sounded like speakers with broken tweeters
).
Bass goes rather low. There is a hump on upper bass and lower midrange. Midrange is smooth and upfront. Treble is smooth and rather extended. The airiness is there when called for, but not the most airy sounding headphone around. Headstage is rather small and typical of a closed headphone. Imaging is mediocre. Instrument separation and layering are also mediocre, but it may have to do with the small sound stage.
Frequency balance is close to what I consider perfect. Smoothness of the midrange and treble is its specialty I guess. Detail wise, I am not so sure, it is not a headphone that throws detail at you, so at times it sounded a bit smoothed over. But on a track that I am familiar with I actually hear people talking in the background that I have not noticed before, so it might be that I am not used to the smoothness of orthodynamic driver. I could use a larger sound stage, but I am not someone who emphasize imaging with headphones, I feel that headphones just can not do a proper sound staging. I also could use a better layering.
Comfort is fine for me. The ear pad can be deeper and seal better though.
I am not sure what to mod for, as it seems pretty good to me for a closed headphone. I think I probably won't be doing anything extreme. Any suggestion on the direction would be welcome.
Edit: On further thought, the dynamic seems compressed compared to other dynamic headphones that I heard, not sure if it is the property of orthodynamic driver. And I think I do hear the resonance, Michael Buble sounded like he is singing into a tin can.