I have stormed through Bioshock and through a part of Dead Space, and
enjoyed their sound-rich atmosphere. (By the way, are there any other
such games ? This appears to be the only games I get excited.) I used
onboard sound (Realtek HD, Azalia 1.0 spec). But now people tell me
that my experience with those games (and other games) would be much
richer if I used a sound card.

I did a search on the Internet. Here are my findings:

-- The main reason of having a sound card in gaming is the surround
sound. This gives one an opportunity to pinpoint the source of sound.
It is not clear to me yet whether onboard sound adapter can provide a
surround sound as well.

-- Sound quality from Realtek HD is almost as good as a sound card (we
are talking about gaming in here, not music or movies).

-- Games like Bioshock use EAX 2.0-5.0, which is a fancy way of saying
that the game engine generates directional sounds and pumps through
2-5 speakers. Quality of sound reproduction improves. (One of the
features of EAX is that the sound can reflect several time in a
corridor from a stone wall or other material, and one can hear that.)

-- There is a separate 5.1 standard (pumping sounds through 5
speakers) to play non-EAX games. The sound card should have a Dolby
surround sound for that; onboard sound cards apparently do not have
it.

-- Creative Labs is a manufacturer of sound cards, and they came out
with an "X-Fi", which is s set of sound technologies, one of them
being EAX effects.

-- Creative Labs is virtually a monopolist on the sound card market,
and they have an XtremeGamer card which is for the gaming (around US
$100). A recent contender is ASUS which came up with a Xonar line of
sound cards. The cheapest but able contender is the "DX" card (around
US$80) (and that's what I recently ordered).

It is still unclear to me whether one can get surround sound (via the
headphones) using only the onboard sound card. I need this function to
play the games such as Dead Space or TF2. It seems to me that the
onboard sound adapter provides such a capability, but I am not sure if
the sound cards have some additional sound technologies which provide
an enhanced sound experience (such as directional sound etc).

On the whole, I've come to the realisation that the immersion depends
heavily on sound atmosphere (gameplay), and this is likely to be the
direction of the development of the future games. Is anybody aware of
the new such games in development (so that I could look forward to
them) ?