599's were my first pair of audiophile headphones. Now look at what I have. Quit while you're ahead and enjoy the 599's, they're great.
Bowernator
HD 58X.
I kept them longer than most headphones I owned (also had 560s, 599, 6xx, 660s, and 800s from Sennheiser, but held onto the 58X the longest), and I went through quite a few trying to find one (or a few) that fit my tastes (I like bass and "fun" sound, but in an open back). Edition XS almost fit this bill for me and was my first planar, but both units I got both had driver buzz/crinkle under bass, so I gave up on those. HD 800S were cool, but far too bass light for me. Dipped my toes back into planars, but with Audeze this time. Got an LCD-GX open box for $600 and damn. With some EQ and HeSuVi, these would vibrate on my head in games and music w/ heavy bass, and the sound... amazing. This led me to getting the 2021 LCD-X for $900, and recently got a Maxwell for wireless gaming. Listening to the LCD-X as we speak, just a wonderful headphone.
I think out of all the headphones I've owned, I held onto my 58X the longest. Great headphone for the money, just a good all rounder.