Well I never heard the X 5, but I guess it is also taste. I not want to try the X 5. First it is a big investment. Second I love the X3 for his musicality. It combines a non aggressive sound, warmth and transparency. I not need more clarity, especially on the "line out". On my headphones it sounds a tag less clear, but on the line out it is just perfect. The bass is even a bit too transparent at times, but as my room is not threatened, this is not a bad thing. I am really enjoying MUSIC, on my headphone, and on my B&W 800 D. Detail and emotion....
I agree it's all a matter of taste.
I really liked the X3 when I had it and sometimes miss the hardware bass/treble control as they sounded very good to me when I used them.
Enjoy what you have if it's working for you.