I've been stuck on X-Fi because of Creative's own stupidity (or whatever you want to call it.)
I hate their lack of driver support for Windows 7/8 but found their software packages still work (even Alchemy - which is awesome for older games.)
Anyways, here is how I'd review them from my own personal experience:
X-Fi - the last great balance between movies/music/games. Great sound for each, has all the EAX junk if you care for that, Creative even put out DTS/DD drivers for Win7 which also work on Win8. Great if you are using a receiver and the game doesn't support multi out through digital or pass thru HDMI.
Anyways, the sound is excellent.
Recon3D - I picked one up hoping to get improved driver support first thing I noticed was game audio was awful. It felt flat, didn't have the pop that my X-Fi had, and eventually I went back to the X-Fi. I didn't bother doing enough research to what they changed hardware wise, but also the powered-AMP didn't drive my cans well enough either. Overall it felt like 3 steps back from X-Fi. My Audigy2 had better bang.
Z-Series - I had a Zx for about two months. They fixed EVERYTHING wrong with gaming audio and the new power AMP drives my new cans better (I too also got the PC350, great headphones.) Anyways, where it fell flat on it's face is Music/Audio. Not sure what they did with the crystalizer but now it sounds far more noisey (by which I mean distortion.) The lows are almost gone hidden by some reverb crap that I couldn't for the life of me figure out how to turn off. The audio quality for anything non-gaming was abysmal. I hit some reviews up and realized just about every one said something similar.
On the Creative side, if you only care for gaming the Z-series is excellent, avoid the Recon3D at all costs.
If you are looking for great movie/music support Recon3D is pretty much all that is left. I can only find the X-Fi Titaniums as used/refurbished.
Avoid any of the lower tier X-Fi (Gamer/Music) series as they are not hardware driven, ie they use CPU cycles for their computation needs. You're basically buying a daughter board to support their software algorithims.
I don't have enough experience with ASUS, but the Xonar DT we put in her system satisfies her needs. When I've used her PC I had no issues with the sound quality (would personally prefer to tinker with the Bass a little but she won't let me.)
Her headphones are the Vengeance 1300s. With onboard they sound flat, awful, with the Xonar (the powered Amp) they sound robust, not as good as my PC350s, but definitely better than any of the <$50 stuff she's had before.