Installing the driver over the old one previously installed will get you nowhere.
Here is how I was able to successfully installed it.
First the best is to figure out which version you need; in my case I have Win 8.1 64-bit so I installed the 64 bit from the installation package instead of it finding out. I would think that If you use the setup.bat install in the base directory that should work but took no chances.
I did not leave the player connected initially when performing the following:
(1) Uninstall the previous version by going to Device Manager, open Sound video and game controllers, right click on the iBasso Mango HiFi Audio Device and uninstall it.
(2) Install the proper version of the driver from the download using setup.exe (folder: 10-24 usb DAC Version1.0 contains both the x86 and x64 folders for 32 and 64-bit drivers, pick the one that is compatible with your windows install)
(3) Connect your player and check the Device Manager. You should see "Mango Device\Mango USB Interface" section without any exclamation mark on it, if you do have exclamation mark, then uninstall and install by right clicking and selecting Update Driver Software and browsing to the directory of your install called "mango_sub", example for me: \10-24 usb DAC Version1.0\x64\mango_usb. It will pick up the audio device driver and install it properly. If you do not have the exclamation mark it means the driver has been properly installed.
(4) Disconnect and reconnect the player.
After all that you should be able to see you USB driver showing up in the Control Panel/Sound section. Make it the default so it will play through your player.
Sorry about the number of instructions but this driver is anything but easy to setup.