Ok.
Basically I want to play my playstation on my monitor.
I got the video part ready since my monitor has support for aspect-ration fix and component input.
Only the sound is the problem. The Ps2 has a optical output.
Since my soundcard doesn't have any optical input port I will buy a budget one which does.
Now, is it possible to reroute the 5.1 optical signal to my primary soundcard's output 5.1 ports? Are these any extra program that let me choose which input and output Windows will handle?

you have a few problems with what youre wanting to attempt. for a PS2, the only media that is encoded in 5.1 are the movie cutscenes, the rest of the media on the disks are in 2 channel stereo, so you would be just as well off with 2 rca cables as you would a single optical cable, as the center, and surround channels are all matrixed from the 2 front channels, when it comes to PS2 gaming anyhow. the second problem is that for the digital 5.1 to work, you need a digital decoder to decode the 5.1 channel cutscenes (a digital surround amplifier/receiver with an optical input would do that fine).

so, if you can get a stereo rca to 1/8" stereo adapter, and connect that beween your sound card and the PS2, that would work fine, as youll still be getting the matrixed 5.1 surround, but at possibly reduced sound quality, another downside is the cut scenes will also only be in analog stereo, instead of the 5.1 youre wanting.

what would also work, is using a digital surround amplifier/receiver for the sound with the optical cable (so you get both the movie and gaming in their expected sound), and use your pc monitor for the visual portion of the PS2, and that should work better even.

edit: as far as a sound card with optical inputs, it should come with the software needed for configuring the input and output channels, the possibility of the movie cutscenes being decoded in 5.1 is probably iffy though, as you would need a digital decoder to decode the 5.1 channel encoding, and it might only come out as 2 channel pcm stereo, at possibly reduced quality, again.