I agree that it is a personal opinion, a matter of taste and probably what you expect. And the advantage is not from 0 to 100 with just flipping in a card. I think we all agree on that.
What I also agree upon is that onboard-chips for home-users have 5.1, some even 7.1, but as on all of my statements, the question is HOW GOOD. I can drive around the world in a Trabbi, but if I had the choice, I would prefer an airplane.
I guess my opinion towards onboard-soundchips, no matter what quality and purpose, is a little preoccupied, as I had a soundcard for my PCs from the very start. In fact, even in times of Quake2 and UT99 I was even banned with my PC from Lanparties, because I could hear things others couldn't and on one LAN I even had to make a duel with a friend, my eyes shut and I still won!
In the 6 months I had to play without it, I felt like my ears were cut off.
I also tested 5.1 and 7.1 systems for a hardware reseller with and without amplifier, with onboard-sound, USB and PCI-soundcard. The winner was pretty obvious for all tests (Gaming, Musik and Cinema).
But again, IMHO this is about priorities.