Headphones

In 2019, in an effort to find a better sound solution for my then-new Sennheiser HD6xx headphones, I ended up purchasing--and falling in love with--the EVGA Nu Audio internal sound card for my computer. This was after trying an Fiio K3 external unit and being wholly unimpressed with it; if I remember correctly, my headphones were rather quiet even on max volume for that device. Generally, I didn't know what I was doing.

Fast-foward, it's been almost five years, and I'm still using the audio card. Unfortunately, I view it as an unwanted crutch: I'm designing the rest of my PC builds around the need to include it, because I fear going without. For context, despite the lackluster community discussion 4-5 years ago ( https://www.reddit.com/r/audiophile/comments/afhmos/nu_audio_new_soundcard_from_evga/ ), the card really does a much better job than its critics suspected; certainly, it has performed much better than the Fiio K3 which was often recommended instead (at that time). Unfortunately, the card is basically unsupported and, as EVGA is basically out of business, I will eventually need something else.

Though I learn a bit more everyday, I regret that I still don't understand a lot about audiophile nomenclature, so comparing this product to others makes me go cross-eyed. These are the specs for this card that I was able to scrape from the site (https://www.evga.com/articles/archive/01281/evga-nu-audio/default.asp ):

Audio DSP:
XMOS xCORE-200
Native DSD Support (up to x256)

Output Configuration:
2 Channel (Analog)
5.1 Channel (Digital via S/PDIF)

Dynamic Range (DNR) / Signal-to-Noise (SNR):
123dB (Stereo Playback)

Playback Format:
Up to 384kHz, 32bit (Stereo)
Up to 192kHz, 24bit (Optical)

Headphone Amp:
16-600ohm (Independent Analog Control)

Maximum Voltage:
8Vrms

Maximum Current:
250mA

I/O:
Stereo Out (RCA L/R)
Headphone Out (6.3mm)
Line-In (3.5mm)
Mic-In (3.5mm)
Optical Out (TOSLINK Passthrough)
Front Panel Header

Premium Components:
DAC - AKM AK4493
ADC - AKM AK5572
OP-AMP (Headphone) - ADI OP275
OP-AMP (Line Out) - ADI AD8056
Capacitors - WIMA, Audio Note(UK), Nichicon
Power Regulators - Texas Instruments TPS7A47/TPS7A33 ultralow-noise power solution

Switchable OP-AMPs:
Headphone, Line out

Which of these specs is important to ensure that I have similar performance for my headphones, with whatever replacement product I choose? Are there any specs I can safely ignore? If you need another product example, I was recently looking at the Fiio K7, as it's about $200 (about what I paid for the EVGA card 4-5 years ago).

P.S. Right now, I use the provided RCA to 3.5mm adapter (https://images.evga.com/products/gallery/712-P1-AN01-KR_XL_2.jpg) to connect to a pair of powered Klipsch desktop speakers. I don't use external speakers much anymore, but I'd like to maintain this versatility. I would plan on doing something similar, unless there's a better way?