> Is It possible to add a SoundBlaster Live PCI card or SoundBlaster 128 PCI card
> in PowerMac G5 to use correctly the mixer IN CD-ROM ? SoundBlaster Live PCI
> card is 3.3V while SoundBlaster 128 PCI card is 5V

PowerMac G5 PCI(-X) is 3.3V, so 5V-only cards won't fit/work. There has been a thread on the topic of SoundBlaster Live on G5, but no replies so far:

https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=12457&forum=11