External DAC vs. your quality processor

As I work on completing the path of music from iMac to Maggies there comes the issue of: Should I consider an external DAC or rely on the DAC in my Krell HTS7.1 to do the work. Perhaps others have dealt with this issue and discovered that, indeed, their processor handles the DAC work very well without the need for an expensive external DAC. Afterall, when you have spent big bucks on a quality processor it would be a shame to find out that you need to shell out more big bucks for a DAC because the processor under-performs. I'm also struggling with Toslink vs. USB.

If you have had similar decisions to make, your comments are welcome.