Think of a product in it's basic elements. A laptop is meant to be portable and because of that, it will never run as cool, fast or cheaply as a desktop computer. Corners are cut.
A gaming sound card like the X-Fi is typically meant for multi-channel audio output as well as hardware acceleration of audio (totally useless feature for anyone with a dual core or faster computer) and weird equalizer tweaks that 95% of users don't know how to use properly (i.e. don't use them). X-Fi cards are the cheapest way to get multi-channel analog audio out of your computer with gamer features.
The first no-no is the DAC chip the X-Fi uses. DAC chips have one job, to convert the digital audio signal into an analog signal that can be fed to speakers/headphones. DAC chips are semiconductors and how efficient their circuitry is affects how good the conversion is. The DAC chip in the X-Fi is a cheap multi-channel DAC that doesn't typically have a wide dynamic range and may muddle the sound if it's fed too much audio or too dynamic audio. DAC chips evolve almost as fast as CPU chips do. 10-15 years ago a DAC chip that might have cost thousands is worthless today. You can take this and realize that onboard audio isn't as bad as it used to be. A lot of newer boards have better or as good DAC chips as X-Fi cards.
The second no-no is the components. Capacitors, resistors, opamps and more. If Creative used quality components, you likely wouldn't be able to afford it. Quality capacitors cost money. There are some botique old Russian military caps that can fetch hundreds of dollars. Those aren't necessary for quality audio but it just shows that there's quite a bit to improve upon with a 1-cent capacitor. Affordable quality ones can cost $1-$5 depending on the type. Resistors run a little cheaper. Opamps are quite similar to DAC chips. Basically, they are a little chip that amplifies a signal; operational amplifier. They can vastly affect quality of audio. Can you guess if Creative used quality ones or cheap ones? Fact: A lot of the better sounding dedicated DAC units don't use opamps at all.
X-Fi sound cards are popular because of misinformation. Companies will always say their product is great, Creative is no exception. X-Fi cards were pretty decent back in the days of BF2, FEAR and a few other games around 2003-2005. Single core CPU's were all we had and offloading audio processing did improve FPS. The problem is, the technology never went anywhere because CPU's went all multi-core. Differences back in the day were maybe 5-10%, these days you would be lucky if you noticed it at all. So, they're low quality, horrible support and no real benefits of usage. Why are they popular? Gamers use a lot of products that have no real purpose, just look at crazy mouse pads, weird looking computer cases, flashing lights, headsets that make them look like they're in a military control room.
So what do you use? There are decent sound cards but their price is pretty out there. Brands like ASUS Xonar and Auzentech have decent ones but to get anything good, you need to go external. USB is where most audiophiles get their audio. One reason to use something external is to make sure your audio components don't use the dirty power generated by the switching power supply in your computer. Sure there's great quality computer power supplies but they're rated for longevity and amperage and reliability, not for a clean signal. Look up R-Core and Torridal power supplies. There's tons of DAC boxes out there and the market is constantly changing, there's tons of "flavor of the month" units and there's quite a few reliable brands. It takes a lot of research and a bit of saving to pull the trigger on your first setup.
I'm kinda running out of steam... it's hot and I dunno what else to say. If you have any specific questions, I can try to help. Look down in this forum a few posts; check out "What makes an excellent sound card" if you've got the time.