I've never owned an Audigy myself, but I'm familiar with them, as two friends have them. So far I am not impressed at all, but Advanced HD might change that (regrattably, I haven't had a chance to play Jedi Knight II with Advanced HD enabled yet).
The Audigy has several of the same shortcomings as the Live does. Sound quality is just noticeably better, and compatability/stability is a little better, but that's about where it ends. The Sensaura engine is awesome (GTXP and Turtle Beach Santa Cruz cards both feature this for 3D positioning), sound quality is good, and it has all the features the Audigy does except for Advanced HD, for a lower price (half that of the Platinum eX). Don't let the Audigy's 24-bit or 100dB SNR claims fool you, I've yet to see a single test where it could actually accomplish that feat.