IMO, for best possible sound quality you should not use a digital volume control. Digital volume controls work by reducing bit depth, 'eating' bits of resolution. Once you go lower than 16 bits it sounds like an Ipod with a weak battery and cracked earphones.
Analog volume controls do not lose resolution or bit-depth, that's why Wadia players have part analog attenuation and part digital attenuation.You are supposed to do most of the attenuation in the analog domains, which is less harmful to sound quality. Read the Wadia owner's manual for an explanation.
DCS and Audio Aero players do 100% analog attenuation and sound superb at all volume levels.
If you really want to experiment with digital attenuation, Behringer sells a suitable and inexpensive unit, the DCX2496. At the price, if it fails your expectations, you will not be too frustrated.
Good luck