Alienware has an amplifier Alienware Graphics Amplifier Review & Rating | PCMag.com
It works great, but the price isn't worth it imo, you also can't use it mobile since it's rather big and heavy.
You can take it to lan parties though.
If you need desktop power, you should buy a desktop pc imo.
Also note amplifier( $300) + gtx 970 ($320) = $620..
I don't know if other brands have an amplifier.