Creative PCI Express X-Fi Xtreme Audio CA0110 & Ubuntu?

Supported in alsa-driver as of version 1.0.15. That is supposed to work.
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If all the same does not work:
1. In Jack see it? If Yes, try cross-connected inputs and outputs
2. Check vendor ID and model in proc
3. Not sure that will definitely help to solve the problem, but for music it is useful to use a realtime kernel. To do this, install the package linux-rt, restart the computer in grub menu there is a point with realtime-kernel. At least get the effect as from ASIO under windows.

linux-rt — package ia so called, is equally successful using apt-get, aptitude or synaptic. It is really a realtime-kernel.
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In this case, the bottom line is that the reduced latency and greatly improved sound quality, regardless of the type of sound card. Particularly noticeable this effect on slower machines. But powerful computers also makes sense.
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Applications for working with audio (JACK to LMMS and Audacity) to push own audio driver to the appropriate optimum state, if available rt-kernel. Ie Ubuntu just put this package, reboot and all.

Also six months ago suffered from this card, then put the package oss4-dkms and it worked. The latest developer builds of OSS supported.
> OSS does not offer.
And what oss are not satisfied? You can also directly connect to pulseaudio instead ALSA, and the als is already using the plugin to connect to pulseaudio, and then all applications that require the als will work as it should. In General, many applications already support the output via the pulse, so that the als can generally remove. I have this scheme works nice.