10 days in with the Phantom cables and good things are happening. Whereas initially the cables were quite lean, they have now 'filled out' (I won't ever be able to explain how these things happen but have accepted the fact that most equipment, including cables, simply need a fair amount of time to burn in properly). The presentation is more relaxed (but still dynamic) and there is now a good level of bass, with good nuance and texture, but without the sort of loudness effect inherent in the NACA5 cables. I find the Phantom treble better than NACA5, with more detail and extension.
I could live happily with either cable but in my current set up and small room (home office, 3 x 3.5 m) I believe the Phantom cables are a better match, primarily because the bass is more controlled/does not 'bloat'. Things may change/improve further over the next couple of weeks, but so far I like what I'm hearing.