OK, it's definitely a DC offset issue. Measuring the balanced output of my interface while playing back that problematic bloc party track, I get a whopping 3.5v of DC:
That's *really* bad - I did a quick scan of some of my library and the worst I could find otherwise was around 0.1vdc on some amateur soundcloud stuff. My best guess is the Topping is either going into DC detection/protection directly, or the DC offset in the signal is causing the amplifier to overload, and the Topping then goes into overload protection. I suppose that's nicer than the Topping just allowing it to happen unnoticed until the front end fries itself. Some clarification from Topping on this would be great.
So, warning: if you're lucky enough to have an interface with a DC-coupled output, (most high end converters, a lot of professional/recording interfaces), take note of what you're playing. If you find the Topping switching itself off and not coming back on until you stop playback - it's probably DC in your source material. Anyone brave enough to play back the Bloc Party track I linked on the last page should be able to recreate this without issue, it does seem to at least be harmless as it goes into protection (at least for now). And to the mastering engineer of this Bloc Party album, which peaked at #3 in UK Albums Charts at one point: give me some of that crack rock you were smoking