First measure stock cable impedance, if it`s under 1 Ohm then You`re good. Well, should be but there are cases where different low-impedance cables gave different results to user.
Seems that most good quality SPOFC cables fit good. I made my own cable from Van Damme XKE Pro-patch. But You can also go for some cheap cables @ eBay & amazon.
Check this post for some info: http://www.head-fi.org/t/623013/new-philips-fidelio-x1/4320#post_10475263
About sound blaster z ...it should be ok but if I remember correctly then its output impedance wasn`t good match. But if it sounds ok to You then no problem. Just test Your stock and beats cable and gear You have. If it was me, I would get some cheap separate dac/amp for music listening. For example cheap ELE EL-D02 with upgraded capacitors fits good.
Edited by CoiL - 1/24/15 at 8:45am