Awesome review! Thank you for taking the time, I'm about to make my first major headphone purchase, I'm struggling to decide on TH-x00 or alpha prime.... however I'm looking to build my own alpha prime with mods, maybe the smartest thing to do is start with TH-x00 to get some real idea of what good headphones sound like, it would end up costing the same by the time I raise a pair of t50rp's to near alpha prime level, I love the idea of modding my own cans... I'm a car guy at heart so I compare this to buying a Nissan GT-R and raising it to Aventadore levels of performance, or just buy the Aventadore, knowing full well it'll just make me want a Bugatti or Koeniggsegg even more...?
I was/am kinda in the same boat. I just picked up some very lightly used X00s for $300 and am blown away by the sound quality. These are my first, what I consider, amazing headphones. Got them primarily because I really want th900s after reading everything about them, but it's a bit scary dropping that kinda coin without know what you're getting!
Knowing what I know now though, I will definitely get the th900s because this is awesome. I want more subbass and soundstage for my endgame and know it'll absolutely be worth it.
I want to have fun with my headphones, and the X00s definitely do that for me. I'm listening to genres I never did before because of how good they sound. Hooked on female vocals now after years of being a total instrumental junky haha.
I have some psb m4u2s, which are regarded as being very similar to the oppo pm-3s, and honestly, I prefer my $80 sony xb90s (iems) to those--and I hate iems haha.
Take this as my subjective experience, but if I was you I'd just go straight to my dream car and prepare to have my mind blown. It's been like hearing music for the very first time with my X00s, can't even comprehend the hifi game, but im going to get there as fast as possible now!
Last thought, the bass on the X00 is awesome. If you like bass, be careful what you get if you do decide to spend big $$$. Hearing and feeling bass frequencies are two very different experiences, and a lot of people here prefer, and recommend the former. Figure out which camp you are in and your choices will become really limited (feeling) or really expanded (hearing).
Good luck, let us know what you decide! A few X00 drops just became active too,FYI.