you can use the Z, however you'll be running your windows volume levels below 25% since the amp is much too strong for them. i'd try out the xonar dx instead which although it doesnt have a powerful amp should work. in a worst case i'd just get a fiio external amp to substitute if its not enough.
the xonar dg is also fine though its not much better than onboard sound in terms of quality (unless you have poor onboard)