I've come over all Shakespearean and its down to the new heart of my system, the Cyrus DAC-X.
It was secondhand and has been performing really well in my system for several weeks now, but we came back from a few days away and it's developed a fault - the left channel is heavily distorted. Tested cables, connections to the pre-amp, different digital inputs, with and without the PSX-R all with the same result - a distorted sounding DAC.
An email's gone off to the Cyrus service dept to check out what to do next, but it'll be a while before they get back, given the UK's plethora of bank holidays at the moment.
Hopefully its not something too expensive!