Hi!
Fist off… I only recommend what I think its the best and what have the great value “economic” and performance wise. Its a DAW working-machine and an investment for the future, not what is the cheapest alternative on the market right now.
I has always believe its more economic in the long run and also better to build a quality machine with great performance, with quality component, that has no problem to keep up the next 3-7 years. After 7 years it will continue to perform, perhaps average; but still pretty good. 
ASUS Motherboard WS -workstation
WS-series or example Dual Xeon Z9PED16 if you going to hook up physical 2x Xeon for 16core -computer
http://www.asus.com/us/Commercial_Servers_Workstations/P9X79_WS/
http://www.asus.com/us/Commercial_Servers_Workstations/P9D_WS/
http://www.asus.com/us/Commercial_Servers_Workstations/Z9PED16/
ASUS NVIDIA
600 Series or 700 series. Take and pick. I use GT 640 myself. ASUS NVIDIA cards = You can’t hear the fan even under load…extremely quiet.
http://www.asus.com/us/Graphics_Cards/NVIDIA_Series_Products/
Intel CPU I7 6core or 8core…or Xtreme or XEON if you have the budget.
http://www.intel.com/content/www/us/en/processors/core/core-i7-processor.html
Intel Core i7-4930K @ 3.40GHz
Intel Core i7-3930K @ 3.20GHz
Intel Xeon E5-2687W v2 @ 3.40GHz
Some like AMD and I think its great that they exist too even though its not for me.
AMD much more cheap then INTEL but even 8 core AMD-cpu get “runover” with simple 4core Intel I7. It is as always, you get what you pay for.
This can be fun for everyone. Check this site to compare “performance” with example you own setup with a new build. You can also check INTEL VS AMD cpu’s, NVIDIA VS ATI etc…
Corsair- memory Vengeance, Dominator all are great series.
http://www.corsair.com/en/memory-by-product-family/dominator-platinum-ddr3-memory.html
You need to read reviews. At least 1333mHz up over 2000mHz. 2000mhz can be good with a new setup.
Install at least 16GB of RAM!
Seasonic - PSU, It doesn’t get better then this!
http://www.seasonicusa.com/NEW_X-series_560-660-760-850.htm
Choose whatever you like from X-series, Gold, Platinum series.
I use Seasonic myself. Its the best PSUs in the world, no doubt! 7 to 5 Years warranty world wide…probably last 20 years. Build with extremely high-quality component, fans etc… and gives you extreme clean power to the computer.
Its like Bugatti, Ferrari, Lamborghini…I think you get the point.
I hope I answered some of your questions.
Best Regards
Freddie