Thanks for the replies, but I'm still where I was when creating this thread.
Did you disable the motherboard's on-board audio, in the BIOS, when you installed the STX?
Have you tried the Unified Xonar drivers?
http://maxedtech.com/asus-xonar-unified-drivers/
Maybe spend $20-$60 for upgrading the STX's 3 op-amps?
What is the make and model of the 600-Ohm headphones.
Do you use the STX's Dolby headphone?
Or do you use the STX more like a DAC/amp?
Yes, I've disabled the on-board audio ever since I've (physically) installed the STX. I've been using Unified Xonar drivers on Windows 10 for as long as I can remember, because I had issues with the ASUS ones when switching to Windows 10. There was no sound output, no matter what I've set the output device to IIRC. Using bootleg drivers feels extremely hacky still. I'm not even talking about booting into safe mode with driver signature enforcement explicitly turned off to be able to install them, nor am I talking about the implied security risk of running software of unknown origin and giving it the highest privileges possible. I'm having more mundane problems with the Unified Xonar drivers: For me the installer more often than not fails to find the STX and refuses to proceed installing. And no, I've not forgotten about the internal power connector when physically installing the card. The last couple time I've had the misfortune to have to reinstall the driver, at some point the installer froze and after rebooting into normal mode suddenly there was sound. Although I've disabled driver updates via Windows Update, Windows still decides to replace the installed driver with the stock ASUS one every now and then. I've also rolled op-amps. I can't exactly remember which ones I'm currently using (if it's not clear by now, I'm not an expert), I just looked up how to improve the sound on the STX when I was bored one day, ordered and swapped the op-amps to whatever was recommended and I was happy with the results (or at least not bothered enough to undo the changes). Lately I've found myself using Linux based operating systems more frequently and while the STX seems to work fine out of the box on most desktop-focused distributions, the sound is somewhat lacking even with tweaked pulseaudio settings and a system-wide equalizer in place. So I'm hoping to get a more "platform-independent experience" with an external DAC + amp, too. Other than that I'm planning to upgrade my PC (switching from Intel to AMD) and I'm toying with the idea of building a mini-ITX system just for the sake of it. Given that there's only one PCIe connector on mini-ITX mainboards, which will be populated with the graphics card, I wouldn't be able to fit the STX in there. There are reasons why I didn't ask how to make the STX sound better. My mind is pretty set on getting rid of the card. The headphones are actually a headset. I didn't bother to mention that, because I didn't want the thread to revolt around that (or the STX
), but it's a Beyerdynamic MMX 300 Manufaktur (2nd gen, 600Ω variant). I doubt I've ever knowingly used anything Dolby. Unfortunately I can't answer your last question, because I simply don't understand it.
You will need a high output voltage if you want to drive a 600 Ohm headphone with the bass boosted.
Perhaps go for a cheaper DAC that has the functions you need and use a separate headphone amp or speaker amp that drives the headphone directly or is that not an option.
What's the budget ?
What's considered high output voltage in this context? I wouldn't mind having a separate headphone amplifier. The setup doesn't have to be portable. I'd even prefer desktop device aesthetics, but that's not a deciding factor at all. My budget is 500€ (about 560$), but just like everyone else, I don't want to spend more than I have to: I don't claim to have above average hearing capabilities, so whatever can provide me a fair bit of bass (without making absolutely everything sound like mud) goes.
The ASUS Xonar STX is a decent DAC. I am not sure why Amir's measured one had that bad results (probably bad drivers, the Uni Xonar solves lot of problems, give it a try) but other individual tests (like on RMAA site) proved it is a good DAC solution for the average people (me and you probably).
If I were you I would buy an Atom amp and use the front line out of the STX but using the UniXonar driver and EqualizerAPO for your bass equalization (be aware, use negative pre gain or better a low-shelf filter or you'll encounter digital clipping).
I earnestly appreciate you, too, taking the time of your day to reply to some random guy on the internet, but I would've also appreciated it if you just assumed I had a legitimate reason for asking for recommendations on a USB DAC and headphone amplifier that can drive 600Ω headphones (with some oomph) for 500€ or less. I mean, I would've asked for tips on how to improve the sound of the STX instead, if that was what I wanted to know.
Whether or not I've actually ever had a legitimate reason may be subject for another debate.