Get an inexpensive sound card with digital audio out. Run optical or coax to the receiver. This will eliminate any signal noise from the computer and bypass the onboard DAC.
For speakers, Behringer Truth 2030P. Don't let the price fool you into thinking they are not good. They have been tested and reviewed to be exceptionally flat and uncolored.
Behringer Truth B2030P | Sweetwater.com
Sub, SVS PB-1000.
This gives you a great near field 2.1 setup with the chops to rock the basement while you work out.