Duh... "Low-Distortion Sine" and "Digital Switching" are not happy bedfellows... You cannot create a 'pure' (for 'pure' read 'low-distortion') sinewave from a device that's going to switch digitally (ie on/off). If you create a sinewave from your 10 or 12-bit component, and you magnify the edge, it'll still have little square-shaped teeth marks in it. Those teeth marks will have sharp square edges... and square edges give high frequency harmonics... so your sine-wave (especially ladder network created types) will be as pure as the driven slush.