This are sole my opinion and may differ form others , in my point of view and that concerns only DSX no DG or DGX only XONAR DSX that has to be kept in mind because there is differences between those .
Xonar DSX generally sounds better then SBZ , more dynamic with better SUB WOOFER performance and generally better BASS performance . The whole audio spectrum High,Mid,BASS are better while performing but keep in mind I listen to DnB , Techno , minimal but also occasionally jazz , blues rock however my mainstream is electronic music .
In games again sounds better the 7.1 really makes difernces but once set to 5.1 I cant say that Xonar is any better here they perform the same so In games that are multichanel ,5.1 posssibly you wont see much differences but in one field Xonar beats SBZ again , amplification , speaker management . Generally Xonar sounds louder then SBZ and that's very notable on my Razer Tiamat 7.1 v2 pure surround headphones.
On this headphones the Xonar sounds much more dynamic and louder and by that I mean over 50 % and that's a lot . I dont know if this is specific to this hp's only but thats what I have so again Xonar performs better in that term (dynamics , loudness,volume) in games.
Software ...well Xonar offers better management , speaker placement and amplification , better DTS NEO functionality which I do use for time to time specially if only 2ch audio is available (chrom) , Kodi (streams with 2 ch audio) The NEO matrix does the job way better then with SBZ.
Connectivity ..well here SBZ beats Xonar as you have dedicated OPT out while Xonar offer 3.5 inch TOS adapter wich goes stupidly in the Back Surround L/R jack so in my case I have here plugged my Logitech Z906 to take advantage of DTS Interactive and NEo but that means now my Tiamat 7.1 are perfoming 5.1 as long as I dont unplug the TOS adapter and re-plug the Tiamat Back Surround Jack ..thats something I don't like.
The Sound Blaster Z in my opinion has better longevity then Xonar , ASUS doesnt give a shit about their customers and devices they produce and sell , while Creative is much , much better and if something goes wrong driver wise and Windows Update , upgrades Creative will fix it for sure quite soon, with ASUS Xonar you could be left in the dark and that is another thing I don't like but I took the risk .
IN other hands If you go for SBZ and never heard DSX performing you will be happy with the SBZ but in my case I already had SBZ and was very satisfied in my gaming rig , wanted to upgrade may 2nd PC a MEDIA pc and I said ..lets take XONAR DSX , I try it out in my gaming PC first ...and it was literally WOOOOW!!! ...WTF!!!! I was really surprised how much better overall XONAR sounded so I left it in my Gaming PC...and then..fck! ...I want that in my MEDIA PC as well ...so wile I still have my SBZ now doing nothing I bought another DSX for my media PC as well . I'll keep the SBZ as backup in case of future Windows Updates and upgrades and ASUS inability and laziness to update the driver software for XONAR DSX rendering the awesome peace of equipment useless.
Something else , hardware wise the SBZ looks way better then Xonar , honestly ..has a nice shielding and it glows RED which I find very cool , in other hand XONAR DSX looks simple , plain nothing exiting about .
Then again I like the way I can customize the XONAR Appearance (SKIN) this one is made by me to match my hp OMEN X900-000nx gaming PC
