I don't agree with all the negative comments here. I am sitting here switching between my HE350 (2 layers of TP), and the Sennheiser HD598 (which I have owned for years). The 350s definitely have great bass and treble (I play acoustic guitar, piano and electric bass). I always thought soundstage difference was a bunch of hooey. But the last couple songs came on and the location was so much more defined in the 350s. I am waiting for parts to do the electronic mod. (https://diyaudioheaven.wordpress.com/headphones/measurements/hifiman/he350/) But to my ears, I really prefer the 350s to the Sennheiser HD598s.
My preference order of the cans I own:
1. HE400i [$400 but dropping fast on Amazon]
2. Senn HD6XX [$200 Massdrop]
3. HE350 [$100 Massdrop]
4. Senn HD598 [$150 Amazon]
5. AKG M220 [$50 Massdrop]
6. Senn HD555 [$100 Amazon]