> I converted flac to .ogg and everything is OK.

Which audio codec? Ogg is just a container format and can contain a multitude of audio encodings, with FLAC being one of them, interestingly.

> I think that mp3 plays via CPU, but .ogg via SBL!

I doubt that the SoundBlaster Live does the decoding of whatever audio encoding is used in your Ogg files.