I have not researched sound cards in a while, but mainly it is in how efficient they are at decoding/encoding anymore. There have not been significant improvements in the consumer grade market. Environmental audio has all but disappeared and standardized audio codecs have improved compatability. I would say if the Live! 5.1 is working there probably isn't much reason to upgrade, unless a new build does not have an open PCI slot for it. In many respects onboard audio (AC97/HD Audio) is up to par with many soundcards.
If you do any audio creation a newer card might handle it a bit faster.