I vhave an Epox 4B2A MB with built-in AC'97 Audio and a Philips A2.500 MMS205 Multimedia Speaker System and I have a few questions for you:

- is this chip an Onboard Sound chip ? If true then how can I properly install it ? I've enabled AC'97 sound from BIOS, RedHat 7.2. had detected it during boot time, configured it, but I 've got no sound output when entering KDE. Before enabling it I got an error during reboot: aumix: cannot open sound-slot-0 or sth like this.

- I tried some C-media drivers but I get an error during make command.

It is an onboard sound chip
I have one, and when I had Redhat, the only way I could get it to work was by configuring the aRts sound driver on KDE. If you go to the KDE control centre, there's something about it there.
It sounds like you have a worse error than that, but that's all I can suggest really. Sorry

I asked Epox about AC97 and they replied me that the chip they provided can output only 2-channel sound. Another thing I've learned, this time by browsing the help file of Avance Logic driver for AC97 is that the aumix channels are default muted and they can be unmuted by an app. What app should I use?

Linux works in misterious ways indeed my fellows: i've disbaled AC97, enabled it, disabled it, enabled it ... installed drivers, uninstalled them, installed them ... and as a surprise last night I found that I HAVE SOOOOUUND.
Stereo, since the chip can't output more but yet a huge step from my mute pc.
For any others stepping in this area: things have a way of working out on themselves.
Is there an AI behind RedHat 7.2. ? One could never tell. The truth is beyond OS !