As far as I know, this will work, but it far from ideal.
The analog inputs on such interfaces (if there are any) are designed for more "perfect" sources (I don't know how else to put it without getting to in depth). A guitar is a very "imperfect one".
There are special kinds of interfaces for this specifically. They are more aimed at musicians, and offten focus on simply being great ADC's, often also having a preamp in them.
I would suggest getting something in the lines of a "built for the job" interface. They often have good DACs and headphoneamps too, but if you are a real audiophile, you could get a cheaper one (like 20-30 USD), and get the Xonar as well.
Personally, I'm not really a fan of ASUS' audio gear, as I feel they tend to not be that great, and use a lot of bs terminology to impress customers, but thats just me.