I was thinking about getting Asus Xonar DX or D2(X), but i heard that there are some problems with sound in the games (but it's not that important, maybe it's just drivers).
Sounds like bad rumors, the Xonar's drivers are one of the best, really stable. You will have less driver related problems in games with a Xonar than with a Creative product.
I want the best sound quality i can get not spending a fortune.
You don't need to spend a fortune, but if you want quality products you shouldn't be looking for "computer speakers", you should be looking at home cinema systems and bookshelf speakers.
Coz someone told me that it's posible only via coaxial out and DX has Optical
That is because Dolby Digital or DTS can only be transmitted through a digital data cable e.g. Fibre optical, coaxial, and HDMI.
so why do I need expensive sound card? The cheap one with digital out should do the thing?
Not all soundcards with digital outputs have the same capabilities, for example most sound cards only support stereo through the digital outputs and can only carry 5.1 streams if the data is pre-encoded prior e.g. DVDs/HD DVDs/Blu-Ray are usually pre-encoded in 5.1 and hence why most sound cards with digital outs can pass these 5.1 channels to the decoder/AV receiver opposed to the usual stereo.
The only way to get Dolby Digital 5.1 or DTS 5.1 though the soundcards outputs in material which isn't pre-encoded such as stereo content e.g. MP3 files, games, downloaded videos, is to purchase a sound card capable of encoding the material in real-time into 5.1 streams ready for the receiver/AV. Only a few sound cards are capable of real time pre-encoding such as, Asus Xonar (D2, D2X), Auzentech X-Plosion, Auzentech X-Meridian, Auzentech/Creative Prelude. There are a few other cards which I can't remember the names of.
coz not all the games are in 5.1, but through analogs i will get 5.1 sound(?).
Using analogue you'll only get PCM stereo. The only way to get 5.1 is to use the receiver's Prologic feature which wills up mix the channels to Prologic 5.1, also you will be unable to get DTS or Dolby, not even in DVDs.
I think that DX is good enough for this speakers or should i move to D2 for triple price for this tiny better quality sound and built-in DTS en/decoder (do i need it?, it's already in z5500)?
The Z-5500's only "decodes" you still need a soundcard to "encode" the data into 5.1 bit streams to so the The Z-5500's can decode it.
You will not hear any difference in sound quality between the D2 and D2X, the difference is in its interface. The D2 is for PCI expansion slots and the D2X is for PCI-Express expansion slots. The DX version can only encode Dolby Digital but not DTS that is why it's cheaper. (bare in mind it can decode DTS just not encode it. It can however encode and decode Dolby Digital)
PS. You talk as if the Z-5500 is this fantastic product, It's like 5 year old piece of hardware, if you're serious about movies you'd invest in a home cinema system and bookshelf speakers and leave the plastic toy looking computer speakers alone.
Edit:
3. Analogue will indeed get you 5.1 sound. That was a... big mistake on darrens part. Of course analogue works in 5.1, or else theres a lot of idiots out there with analogue speaker sets! analogue just doesnt sound as good as digital
I hold my hands up; I should have been more specific. I meant that you can't get Dolby 5.1 or DTS 5.1 bit streams through analogue.
