PCPartPicker part list / Price breakdown by merchant
i7 - 6950X 10 cores, 20 threads, overclockable easy
Good liquid cooler for CPU
MSI motherboard (128GB RAM support)
64GB of RAM (with a 9k budget you can do anything really
Samsung 4TB SSD will be enough storage for pretty much anything, as well as having the blazing speed of an SSD
two EVGA GTX 1080s in SLI. A single 1080 is amazing for any game, but two 1080s is completely overkill which of course is what you want when you have a 9k budget XD
Corsair 750D case with a window :D
850 W gold efficiency power supply
Optical Drive
Windows 10 Pro 64Bit
Good Sound Card for your speakers
Wired Networking card with up to 10 gigabits per second speeds
wireless adapter (if he won't be using wifi then take it off probably)
140mm fan
two 24" monitors that still have the response speed (2ms) to game and 1 27" monitor with 1ms response time for main monitor
K95 wired keyboard with LEDS :D
Logitech Mouse (newer one)
HyperX Cloud II headset with microphone
Logitech 5.1 Surround Sound speakers.
still 2500 dollars left over or something like that