How do I record music with my asus xonar d2x sound card
How do record music from my hifi with d2x xonar sound card
That card has a few inputs. Get yourself a recording software. Connect your hi-fi using an analog output to the CD/Aux input on the card or use the SPDIF output on your hi-fi to feed your SPDIF input on the card.
There are cards out there better suited for recording. Your card is primarily an output card... made for playback of audio. It can record audio though. You just need to find a recording software. Then tell your software to use the Asus card as the primary recording device. You may have to do that in Windows Control Panel/Sounds also.
I've really only used the professional ones like Cubase/Cakewalk/Soundforge/Vegas. They can be expensive. I am sure there are cheaper solutions and maybe even free ones that can accomplish what you want.
Your soundcard may have even come with one. Many of those are free trial versions that expire though.
Sound Recorder in Win XP will let you do 30 second recordings. Sound Recorder in Windows 7 I think will let you record in 1 minute increments. You can use these to test your setup/connectivity