Average users don't even need a soundcard/DAC. Only those who think they need an upgrade "need" them.
I just upgraded- using z906 with soundblaster z's - my take - have not fully tested yet, but sound and dialogue are noticeably crisper, punchier and clearer.
However, it is not a "heaven and hell" kinda difference. That said, z906s are not exactly audiophile speakers, and I wonder what a set of audio engines will sound like.
Conclusion- get a budget but well rated soundcard to test first- don't start off with titanium hd or zxr. Maybe the asus xonar dx / dgx or even the sound blaster z if you can find it for 60usd on amazon. At the end of the day hearing is subjective. In my case, definitely no regret going for the soundblaster z.
Up to each one to decide. However it is recommended to go and listen to the differences between the two.

