Nope. ( Ok ok I punish myself: r/InclusiveOr 
)
In this context, the diode avoids the “conflict” between two power sourcers when you power the board from USB and from the GPIO connector AT THE SAME TIME. Ok, it will also avoid polarity errors, but this should not be an issue in a DIY device (I mean, if you can burn the card twice in that way, you deserve it 
)
So, if you’re absolutely sure that you’ll never EVER plug another power source into the rPI while it’s powered from the GPIO port, and that you’ll never plug your supply backward, then you can go without diode.
When I read the word “audiophile” my bullshit meter gets instantly overloaded. One day I’ll write about my fantastic audiophile grade (i mean REALLY EXPENSIVE) shielded heavy cables and my ban from more than one local audiophile community )
But hey, who am I to keep you from spending 50€ or more for a less-than-10-euro power supply?