I haven't used optical out yet, maybe not.but it's just a matter of tests and ears. You have both, sound card and onboard solution, try them. I was sceptical too when I first bought my auzentech, I've got a decent chip on one my previous board but there was differences between them, on the sharpness and the most of it, sounds ,on tunes I listened a thousand times, I've never heard.
"Oh there was a bass here, never heard this bell before,..and more
For me, if you can't hear a large spectrum of sound, the soundcard could be useless. In oppostion, I'll never buy a 150$ soundcard for listening 128kbits MP3, on 15$ speakers.