So I got into good headphones in 2008 when I bought the Sennheiser HD 555 and even to this day still impressed how well it sounds compared to all those $20 headphones I used to use all my life.
Fast forward 10 years later I got my HD 58X today from massdrop. All I can say is the sound quality is improved but nowhere near close to what the improvement was going from $20 throw away headphones to the HD 555. I am just going to class this as a $300 headphones and at that point the diminishing return is quite strong when compared to what the HD 555 offers for the price of $90 at the time I purchased it. I am powering it with a Xonar DG sound card
What I noticed about the 58X and what I can say about reaching the audiophile stage of music when compared to my HD 555 is that while not a huge leap in upgrade the 58X sounds more true to life, it puts me closer to the music and it brings it more true to life, it is capable of this holier type of sennheiser sound it is very dark which is how I like it. The distance instruments and the precision it reproduces everything at is quite something.
My dream was to own a HD 600 but this will have to do since I heard it is just like an HD 600 but with more sound stage and better bass.
I am super duper happy with my 58X but I wonder if the grill is aluminum
There is something super interesting I must mention, the HD58X sounds LARGER and BIGGER than the HD 555. Basically its like going from a small swimming pool to an ocean. The HD 555 sounds like everything is infront of you in a smaller ball, where as the 58X sounds like you are in the middle of everything this is especially noticeable with Bob Marley and The Wailers sound tracks.