Windows audio provides 8 channels, that's 7.1 : Left, Right, Center, Sub, Rear Left, Rear Right, Side Left, Side Right.
All you need then is an 8 channels USB DAC like MiniDSP U-DAC8 (or a soundcard) and of course 8 power amps and speakers.
HT Omega (excellent quality) - has been making improvements on an 8 channel ClARO HALO XT sound card for nearly a decade. This is an analog out duel card PCI sound-card.
I believe sound-blaster also makes an 8 channel card. Prob many more co's as well.
The only negative aspect to using PC sound-cards for HT or 2 channel music etc is the HT Omega adjustments to output freq's to minimize computer fan noise. Although i challenge anybody to identify the fan noise or compensation in the listening room sound balance.
HT OMEGA CLARO HALO XT specs
24-bit / 192kHz AK4396VF 120dB DAC
24-bit / 192kHz AK535BVF ADC
TI 128dB Headphone Amplifier with user selectable high/low impedance settings
5.1ch Optical / 8ch (7.1) Analog Output
Professional Grade RCA Connectors with included lock nuts
Swappable Front and Headphone Out OPAMP Socket
Anti-pop Protection Circuitry
Advanced Front Panel Audio Support with selectable automatic mute feature
Two 2-pin connectors for Coaxial Digital Input/Output with CA-1 cable
External MIDI Device support with CA-2 bracket available separately
The question i have now: can you take a movie recorded in Dolby Atmos run it through a 7.1/2 sound card and then back into a Dolby Atmos Pre/Pro with minimal, to no, sound degradation