You tried many amps and non of them worked? So now you listening them without an amp?
After various tests of amplifiers, I listened without an amplifier. The equalizer compensated for those frequencies where the “T60RP” had gaps.
Then the interconnect cable frayed, with careful use it lasted 1 year.
During the repair process, I realized that the DT770/990 were made better, more intelligently)) I mean the structure of the can - the DT can closes tightly, the space is the same size.
With the T60RP, you can twist the can with different strengths, there is a circuit board inside the right can, air blows from the right can through the connector, the speakers themselves have a clear noticeable imbalance.
I thought about the stage for a long time, the bass sounds wide and large, and other frequencies sound narrower, due to this it seems that the stage is narrow, but first of all, it is not uniform
But the DT770/990, on the contrary, has a wide and uniform stage and velor rather than leatherette. And the weight is 100 grams less..
The advantage of the T50/60/5050 is that they can play loudly, this gives an advantage in bass power, if you add it with an equalizer, there is no booming when the form is open. And that’s all, then there are only compromises and problems.
I sold the T60RP, in my opinion Fostex are controversial headphones.