I would say anything older than 3 Years has probably been surpassed. New Cheap Sound Cards are around £20-30 and can make a nice difference on cheaper headphones or speakers.
Anything older than 3 years has been surpassed? You have surely have got to be kidding?
I'm surprised. Especially coming from someone that has good headphones, and a Titanium HD, if indeed you do have a HD that is. I'm assuming you do, as the Titanium is not far off 4 years old.
Quite a lot of people have found that a Xonar DG sounds better than the onboard audio of their motherboard, and in some cases, a top of the line motherboard.
There are quite a few people that find the DG sounds poor in comparison an X-Fi, which 6-7 years old now. There also are people who are still using an Audigy 2, that find it better than modern onboard audio, and that card is about 8/9 years old now.
Onboard audio has only surpassed very old cards, such as the SB Live!, or those cheap unbranded ones.
There are people who cannot tell a difference between their onboard audio and a sound card, such as a Xonar D1/X, and in some cases a D2/X. I've seen some guy say he found both a Xonar Essence and an X-Fi Titanium HD, no better than his onboard audio.
It's not because onboard audio is as good as such sound cards. It's either because people are not using anything good enough to allow them to hear that difference, or they cannot differentiate between varying quality of sounds.
There are quite a lot of people that use cheaper 2.1/5.1 PC speakers, and find the bass really good. It isn't good at all, it's rubbish. If said people can't tell between poor quality bass, and good quality bass, then any argument they put forward, that modern onboard audio solutions are as good as the majority of sound cards, that doesn't hold a lot of water, does it.