Every time you mention inverting phase or phase
splitting to the semi technical audiophile, they go into
shock.
I have another hypothesis which occurs when the stage
is not being used for much gain:
It is my experience that at low and unity gains, a lot of
op amps are on the edge of oscillation. Over the years
I have made a number of bad sounding circuits (no, not
ones you've seen) and many of them were bad sounding
not because they were oscillating, but because they were
near the edge. If I opened up the feedback gain, they
got better as they moved farther from the edge.
As a result, whenever I use op amps in an audio circuit, which
is not often, I make sure that I either use up or throw away
about 20 dB of open loop gain. If the circuit has a gain of
10 or greater, this is automatically achieved.
If the circuit has less than 20 dB gain, I toss some away.
With an inverting amp, a resistor from the - input to ground
will do it. If not, then resistance from both + and - to
ground is used.
Works like glue....
