in terms of hardware, dkara has an additional line-in and slightly less noise while the xonar dg has a rather strong headphone amplifier.
in terms of software, the dg has dolby headphone (virtual surround) for headphones. it looks like both have functions for karaoke and similar but i'm not sure (asus didnt list it on their specs pages) if the dkara has any features for vocal recording above and beyond what the dg has.
in short: the xonar dg is a gaming card, the dkara is a vocal recording card. either would work however if you plan on gaming i'd get the dg for virtual surround sound