I used to own a Sound Blaster Z. The Z and ZX are the same card, except that the Z does not come with the audio control module that sits on your desk. To be honest, it is an average sound card at best. I also found the headphone amp on it to be rather weak as well. It struggles at higher volumes. The lower bass and upper treble lose focus when more volume is used. It just ends up sounding far too slow. I would suggest you return it, and get yourself an HT OMEGA Claro Halo instead. You will get far more power, and much better sound quality compared to the ZX card. There honestly is no comparison. The Claro Halo is currently selling for 160 at newegg, which is 40 bucks off.
http://www.newegg.com/Product/Product.aspx?Item=N82E16829271004&cm_re=ht_claro_halo-_-29-271-004-_-Product
http://www.newegg.com/Product/Product.aspx?Item=N82E16829271004&cm_re=ht_claro_halo-_-29-271-004-_-Product