stv - Planning on getting a Fidelio X1, Sony MA500, K702 (or variants) or even a Denon D7000 if I can prise it out of my uncle's hands. Don't have a soundcard as yet though. But I'm surprised people say to get a very cheap DAC/Soundcard (DX) and then externally amplify it with quality amps like the O2 etc - surely though, the superior source components on the STX say must count for something?
A DAC does not need to be expensive these days to sound excellent. Components (DAC chip, op amps, etc.) with very good specs are available for as low as $1 or even less, and these cards are manufactured in large quantities, making their production much more cost-efficient than that of "boutique" audiophile products. The frequently recommended ODAC (comparable measured performance to the Xonar cards) could probably cost less than $50 if it was mass-produced in China like the sound cards are. With the STX, you pay extra price for the headphone amplifier you will not even use, and also for marketing reasons ("high end" products usually have a higher profit margin, while budget ones are sold almost cheaper than it costs to manufacture them, because they are used mainly to gain market share from the competitors). According to my tests, the DAC on the STX has some (minor) advantages in certain aspects (particularly SNR/dynamic range, but the DX is already more than good enough for CD quality audio), but it is surprisingly also worse in others (for example, it clips inter-sample peaks at maximum volume, while the DX does not). The most significant difference is that the PCM1792A (STX) has a different digital reconstruction filter with a linear phase response, while the CS4398 (DX) is minimum(-ish) phase; some people think this can make an audible difference (although there is no general consensus on which one is better), but under controlled conditions most simply cannot tell them apart. Also, the STX has an EMI shield over the analog output section, which might make a useful differences in some computers (it does not in mine, but I do not have a high end GPU to produce a large amount of EMI). Maybe it is less sensitive to the quality of the power supply in the PC as well, but that is purely a guess, rather than something of which I have actual evidence.
To summarize, if you already have the DX, and do not experience any interference issues at all (high pitched noise, buzz, or other artifacts audible when no sound is playing, especially under system activity, such as moving the mouse, scrolling, playing a game, etc.), then sticking with your current card and buying an external amplifier would make sense. Otherwise, an external DAC with optical S/PDIF input would solve the problem, and you would still be able to use the DSP features of the sound card. Of course, it is still possible that a DAC upgrade would give the impression of a
subjective improvement, but note that is surprisingly difficult to make a reliable subjective comparison without issues unrelated to real sound quality (for example, slight level mismatches, or the listener being biased in favor of one of the products).
Regarding amplifiers, if you do not have galvanic isolation from the ground of the PC (that is, you are using something other than an external DAC with S/PDIF or isolated USB input), I recommend a non-grounded amplifier like the O2 or the Magni. I think the Little Dot amplifiers are grounded, and that is a frequent source of interference problems in PC based setups. But if you really want a tube amplifier, then get the Little Dot, try it, and buy an external DAC if necessary.
By the way, "techboy" is
very biased against the STX amplifier (it looks like a lot of his posts are bashing it in one-line comments, and when questioned on it, he tends to disappear), so you can safely ignore his advice. Regardless, the STX is not what I recommend anyway, unless, like me, you have some high-ish impedance but not extremely hard to drive headphones it is best suited to driving, and want to keep the setup simple.
