I would like to ask what are your guidelines in determining your next purchase/upgrade?
Identify bottlenecks and tackle their causes.
I used to mostly listen to headphones on the PC, so I got a soundcard that would do a good job driving those HD580s and would take the front panel connector - the then-new Audigy FX it was.
Got a mixer and misc. microphones and wasn't entirely happy with the ADC any more (decent enough SNR if you avoid multiples of 44.1 kHz, but too much digital filter passband ripple for my liking). Ended up going with a Xonar D1 for that stuff. (Later found a D2 as well, but my PC won't take that without removing the shield, and the drivers seemed to be, if anything, even more quirky.)
Over the years I gravitated more and more towards speakers. My previous entry-level active monitors had been decent enough as a "second fiddle" with low enough noise (though one had a noticeable buzz and the other had had issues with the woofer dropping out sporadically over the years) but they were substantially lacking in bass, and their tonality would shift quite substantially when I'd move my head up and down. So after 13 years of faithful service I got some much fancier ones instead (K+H O110). The difference in bass, clarity and level handling was astounding, plus no more major irregularities in the vertical. That left me with level handling and dispersion basically sorted.
Now I had the speakers up on desk stands but that was about it as far as my little listening corner goes. I eventually bit the bullet and finally got some absorbers (for back and side wall plus melamine corner bass traps) as a first step in tackling the room acoustics. Measurements only seem to show a moderate effect on reverb time, but in person the effect is quite pronounced. Much better sound again (I noticed I have a much easier time hearing the differences between microphones, too), though it looks like reverb times may now be slightly uneven, being lowest in the midrange.
Next up - a real bass trap or two, maybe a sub or two to round out the lowest octave/s (though I wouldn't say I feel like I'm missing much of anything right now). One of my K+Hs also has a minor buzz that I should get sorted (not that bad and probably a dead electrolytic). Hiss level is generally low enough. PC could be a tad quieter still, despite the blanket, but picking out parts for a new one is an ongoing project anyway. There's an acoustic disturbance between the speakers a.k.a. a monitor that I don't know how to optimize (have thought about making a "sound collar" out of melamine foam, not sure that would help).