Try Lynx Studio Technology, M-Audio or RME-Audio for hi-end soundcards.
For USB to Digital Coax/RCA interface converters;
Xitel Pro-HiFi-Link or Empirical Audio USB Off-Ramp & Freeway.
For USB to Digital Coax/RCA interface converters;
Xitel Pro-HiFi-Link or Empirical Audio USB Off-Ramp & Freeway.