Now I think we have nailed the problem with the latest USB development. In piCorePlayer 1.15e the USB audio is now as good as with piCorePlayer 1.15c and the I2S audio cards problems and the analog audio is fixed as well.
So please try piCorePlayer 1.15e.
The pCP Team
Paul, Greg, Ralphy and Steen
Older versions of piCorePlayer may not be compatible with the newer versions of the Raspberry Pi. You need to review the Release notes to determine when the support for your particular Raspberry Pi was added. It is safer to use the latest version of piCorePlayer as it will be compatible with the latest version of the Raspberry Pi.