I've tried and current own a lot of DACs. I don't want to mention the brands here to respect those manufacturers. I am confident that a standalone DACs costing as much as WA7 is not more musical or have significantly better sound than the internal DAC on WA7. We're talking about sound alone, not all the bells and whistles standalone DACs have. :) WA7d feature optical (TOSLINK) input so out from your sound card would work. The RCA jacks are input on WA7d so no...
I urge/challenge everyone to compare WA7's internal DAC against DACs costing up to $999 on sound alone. You'll be surprised and pleased to know how well WA7's internal DAC stacks up. Just use the analog RCA input on back of WA7 and switch to RCA on the 3-postiion switch. This will turn WA7 into standalone headphone amplifier.
Ask yourself if you're enjoying music or are you just hearing sound.
We can talk DAC chips all day and name drop parts brands, but at the end of the day it's the final result that matters - the music. I urge you to give WDS-1 a try. We don't make products with fancy parts to catch eyeballs. We design and build solid, tried and true, no gimmicks, timeless products.