I've just bought one of these (Asus Xonar DX PCIE 7.1), so a quick necro just to review.
The sound quality is noticeably better than my RoG motherboard (probably listening to voice is the easiest way to evaluate).
It needs a floppy connector to power it, one comes in the box.
They don't mate at all and the thing flops about and doesn't make a good connection (the card will complain if it can't see 5volts here). Maybe I'll add some glue to fix this later
The ASUS drivers are still being updated and I saw Win10 64bit ones on there.
Before install I disabled my motherboard sound hardware, but the ASUS install still hung, complained about not being able to see a soundcard and required a reset.
It had actually loaded the drivers and it worked, but not the control application
A second install loaded the application, but don't bother with it, it is a steaming pile of crap and looks like it was designed by a five year old.
an alternative is the xonar unified drivers
http://maxedtech.com/