The Asus Xonar DGX 5.1 card has been reduced to £20.99 on amazon. Would this be much of an upgrade from on board audio? I currently have the latest Asus Z87 Pro motherboard, which has PCIe 3.0 slots, would this still be compatible if its 1.0? Always wanted a card but not sure if it would be noticeable, thanks!
It depends on what you're using for sound - are you using headphones, speakers, earphones, SPDIF, optical etc? The DG has a headphone amp, and so will be nice if you've got a big pair of studio headphones, but of less use with earphones or speakers. The quality will be better than nearly any on-board, including your motherboard. PCIe 3.0 is backwards compatible all the way, so a PCIe 1.0 add-in board will work in a PCIe 3.0 slot.
Currently a mid range pair of stereo gaming headphones and thinking of possibly grading to 5.1 speakers from current 2.1 Logitech set. More importantly I have the HAF X case so I want to fill it up a bit more as it looks rather empty!
In which case, it's certainly worth a go, they've got virtual surround for your stereo headphones which is rather good in FPS and such for positional audio (better than 5.1 or 7.1 headphones) as well, and the amp and signature will be better than onboard.