I tried for a year to love the T5ps. The are super comfortable, really easy to drive, and the sound quality and stage are both fantastic. Unfortunately, the sounds was really 'thin' to my ears, and the highs were just too much. The Ts and Ss on vocals were almost painful. I got the Conductor specifically to try and darken them - it helped, but not enough. Eventually I just gave up (about to sell them.)
Didn't consider the TH900 mostly it looked like they didn't do a good job isolating. Love to try them some day though.
The T5ps are really classical music headphones, and for that they are amazing since you need a good quantity of treble in classical music to make it sing. Since 99% of what I listen to is Classical, I love them...plus they are comfortable and light, which is great for portability (i.e., my go-to portable headphones). A darker sounding portable headphone amp (like the Ray Samuels amps or ALO amp with the bass knob) is a must if you want to listen to anything other than classical.