Edorr gave a good suggestion, that is if you use Jriver. As I understand it, Jriver (ver. 17 and above) processes digital at 64 bit so if you select the Internal Volume option you can reduce volume as much as you want without any impact on the 24 or 16 bit audio signal. I am currently using this option and so far it beats my passive and tube pre.
My findings as well, Hew. I'm using JRiver MC 18 as playback software via its internal digital volume control to great effect. The trick is to output in 24 bit(most modern DAC's can accommodate this bitdepth) regardless of whether one only plays 16 bit files, whereby the 8 extra bits gives you 48dB attenuation headroom until it impacts on the 16 bit material. Though my speakers are fairly efficient(94dB), counter-acted to some degree perhaps by my poweramp's rather low 21dB gain, I never attenuate below -48dB for serious listening and as such, in theory at least, has full resolution left intact for most of my music library.
That's all simplistic numbers, admittedly, but numbers nonetheless that seems to evade many of the critics of digital attenuation where they speak of "loss of resolution." Even if there were borderline limits being crossed(i.e.: the signal being digitally modified compared to its source reference) - again, theoretically - I simply ask this of the ones opposed to digital attenuation: try using your ears exclusively, and not least freed of preconceived notions, before jabbering on about the limits of this solution. Such steadfast criticizing moreover and oftentimes seems to be blatantly unaware of the inherent shortcomings of analogue attenuation in itself, not to speak of what follows with the whole of components that steps into the signal path here + cables, that a capable reference to proper implementation of digital attenuation is hardly at play, so to speak. But of course, this remark also sidesteps what's most important, namely listening with an open mind.
For now I'd even propose that what many hear as "shortcomings" with digital attenuation may in fact equate a lack of coloration, saying more about the added character that comes from analogue attenuation(and all that follows) than any signature of the former. My findings, compared to analogue solutions in general, from using the internal digital volume control in JRiver MC18 is that of a more organic, unrestrained and natural presentation - all of which in my mind even accumulates into a more, yes, analogue sound, though I'd prefer to simply call it more 'natural.'