So today I tried out the Xonar U7, so I can finally give some first impressions of the U7, and compare it to the Creative X-Fi I talked about yesterday. Both are priced about the same so they're close competitors in the USB/PC DAC market (although the X-Fi is stereo while the U7 also has 7.1 surround options, but I'm only interested in stereo).
Besides the U7, I also tried out two Fiio amps with the DACs, namely the A3 (formerly E11K) and the E12A (which has a Muses02 opamp), just to see if they sound better than using the standard amps in the DAC's headphone outputs. I connected the amps to the DACs via the RCA outputs. Oh, and all the time I've used my HD 650 Sennheiser headphone to listen.
So let's start with the U7. I think it's pretty similar to the Phoebus, it's been a while since I've used that one but it uses the exact same software and as I remember it sounded quite similar to the U7, although perhaps the Phoebus was a bit warmer. I don't believe the Phoebus had an integrated headphone amp though (the U7 does), although I might be mistaken. I'd say the U7 amp, which is 150 Ohm rated, is powerful enough to power the 300+ Ohm HD650, but it's of course not as good for the 650 as, say, the amp in the STX (which can power up to 600 Ohms).
Now let's compare to the Creative X-Fi HD. The U7 has more punch in the bass for sure (the X-Fi's bass is a little thin at default), although I think it has less treble presence, which makes the sound perhaps a little more relaxed and a little thinner (though the punchiness makes up for that a bit). The U7 also has a more "analog" sound, as there's a lot more timbre to the sounds and instruments. However, it's not exactly the best sounding timbre I've heard, it somehow sounds slightly distorted overall, and it's hard to put into words but it's like taking a pretty natural sounding recording and processing it to make it sound a bit more precise and tight, but maybe a bit too tight. It's actually a sound signature that's common with the Xonar sound cards I believe (even the STX has it, although the STX has a more refined sound to it and sounds more natural and warmer). I do kinda like some aspects of its timbre and the tight sound, but it's not my most favorite sound signature I must say.
So the U7 and X-Fi both have their advantages and disadvantages. I think the main advantage of the U7 is the versatility, and it's the better card for those who want a lot of surround options or who like a tighter and punchier sound for their music, games and movies. The X-Fi also has surround options, but only virtual surround. It's more a stereo card for music, but even with its default settings it's still very suitable for games and movies because of its clear sound, especially when using speakers or open-back headphones. In my case, at least for music (and I think also games and movies) I prefer the X-Fi sound, especially for longer listening periods (I like the U7 sound too, but it's maybe a bit "too much" for long listening periods, especially when using the Dolby app and Dolby headphone). The X-Fi also sounds more "musical" to me - it has a bit more "liveliness" and dynamic to the sound, and the U7 while technically very good sounding, it sounds a bit clinical with music, so it's primarily a card for gaming and movies.
People do sometimes criticize Creative products, I haven't owned many products by them but they do of course have a lot of experience in making PC sound cards (a lot more than Asus), and while making this card they did know what they're doing, and the result I must say is excellent. The Asus I wouldn't quite call "excellent", but it's pretty good too. They're both very good cards for the price at least (some flaws, but nothing that really disturbed me, and overall they're way better than you'd expect in this price range) and if you're using onboard audio it's definitely a big step-up, if you care about your audio that is.
Ok that was a bit long, so I'll be short about using a Fiio amp with these sound cards: not really worth it. It does make the sound a little bit better sometimes, and more so with the E12A, but it's not a very noticable difference so imo not worth the extra money. I'd say both integrated amps in the sound cards are good enough, even for powering a high impedance phone like the HD 650. Although the X-Fi wins here again because it has a bit stronger amp (up to 300 Ohms i believe). (And it also has a 1/4 inch headphone jack for my 650's so that's another plus.)
