What the firmware actually changes
Flashing the so-called gold brick firmware only changes the tuning. Because the hardware itself does not change, it will not magically raise the player’s overall technical performance. In practice, it is closer to applying an EQ-style tonal shift.
How to flash it
The matching firmware for each supported model can be found on mrwalkman.com. The author provides a free download through Mega.
After downloading, you will get a compressed archive containing two folders: Installation and StockRevert. Use the files in Installation to flash the firmware, and use StockRevert if you want to return to the factory firmware.
Inside the Installation folder, connect the player to your computer and turn on Mass Storage Device Mode, then run Walkman_One_ZX300_(01.10).exe to start the automatic flashing process. Different models use different file names, so use the one that matches your device.
Once the process finishes, the player will reboot automatically. After that, you can choose to flash an additional sound package. The WM1Z package is the one usually recommended, and the flashing method is the same.
What changes in use
Compared with the stock firmware, the gold brick firmware sounds warmer and denser, with a tidier soundstage and some improvement in dynamics. In day-to-day use, it behaves almost the same as the original firmware, so you can basically use it the same way.
When the player starts up, flipping the HOLD switch can enter V2 PLUS Mode. This mode is more power-efficient, but it also comes with some odd bugs, so Normal Mode is the safer option.