The Asus sound cards are extremely high quality, no need to mention frequency ranges. It's a given that they meet the specs.
Asus uses C-Media sound chips. They do not design their own chips. C-Media may produce a version of their product for Asus exclusivley, but they are C-Media devices.
Current CPUs laugh at audio loads. That may have been a concern 10 years ago.
That statement does not counter the
fact that onboard sound devices, sharing the memory bus, require more CPU time (running time, and dead time due to locking the bus), and
cannot run in parallel to the CPU like a dedicated sound card, in a separate bus can.
As to how much an impact that is will vary from application to application. In a DAW environment where you are sampling and mixing at 24 bit/192Khz, you will notice the difference, as an example.