How to Connect Integrated Amplifier to PC??

Howdy. I have an Onkyo TR-NX676 Driving my bookshelf speakers currently from my PC using a 3.5 mm to RCA adapter. I recently bough the Focal Theva's and I wanted a better, more stereo focused integrated amp or similar solution. I am not against a piecewise solution. Is the best way to connect HDMI ARC? Do I need to buy a Sound card? Any recommendations would be great! I am looking to stay under $750. Might be able to stretch for the perfect piece! Thanks!