With respect to the topic of this post and the issue I personally experienced, the firmware appears to have corrected the problem. Thus logically, it was a software related issue.
Has it done so for every user that experienced issues, and irrespective of the source? That's a rhetorical question, as obviously no one knows the answer to that question. So no, I do not agree that it is logical to extrapolate from your single, anecdotal experience, that it was therefore a software issue.
Even if the software patch were to prove 100% effective in eliminating the problem, it doesn't mean that there isn't an underlying hardware problem. And again, if it was a pure software issue, how could it possibly have taken so long to resolve, and why would Denefrips still be hedging (i.e. "reduced")?
I would argue that the available evidence continues to strongly suggest that it is a hardware issue, and that efforts have been made to mitigate the problem through a much less expensive approach than a recall and hardware fix.
As for issues relating to the quality of the sound produced by Denfarips DACs, I have made no disparaging comments beyond the narrow topic that we are discussing.