You can use the Google USB driver on the Nexus 6 to connect your computer to the mobile device. Simple follow the instruction below in order to get the Nexus 6 to connect to your computer. The instructions are easy enough to follow. You can find the Nexus 9 on this website as well and it uses the same driver and process as the Nexus 6 USB driver.Its a Google driver.
Nexus 6 USB Driver
Download the Google USB driver firstly from this website below and extract the file to a directory which you know, onto your computer. The USB driver file is normally called (latest_usb_driver_windows.zip). Now you will need to open your device manager in order to update the driver for the device which would normally be showing an error.
1. Click Start menu and right-click on Computer.
2. Click Manage.
3. Click Device Manager in left pane.
4. In Device Manager window, expand categories and locate the device
5. Right-click on the device name and select Update Driver Software
6. Click on Browse to find the location of the downloaded driver file.
7. Find the files you had just extracted for the Google USB driver and click on the .inf file;
8. Click on Next button to install the driver.