Im surrently using z5500 on an onboard soundcard and I find the sound crappy and thin when listening to music. Which of this two (Auzentech x-plosion vs Creative x-fi Music) would help improve the sound quality in terms of music playback. I will sue my setup for 70% audio and 305 movies, not a gamer here.
I was using an intel 845 chipset with onboard sound to connect to the Z5500's and the experience was horrid. After a lot of study, went in for the Auzentech X-plosion 5.1 DTS. WOW. the Z5500 literally came alive. Now i use the optical cable to connect the z5500 with the sound card. Long story short.........the best bet. GO AUZENTECH !!!
For music you'd better off with this card. It uses the newest chipset and has gotten very good reviews. I have the HT Omega Claro, which uses the same chip and a definite noticeable difference from the onboard card but it's more expensive than the Bluegear. Google reviews of the Bluegear, think you'll find them interesting.