I know of 4 currently on the market with the least expensive >$1000. Or are you thinking of AVRs?
Here are some multi-channel DAC's that can do at least 8 analog channels of output:
StarTech ICUSBAUDIO7D - $34
Creative Sound Blaster X3 - $119
ESI Gigaport HD+ - $170
ASUS Xonar U7 MKII - $215
Creative Sound Blaster Audigy2 NX - $265
Tascam US-16x08 - $270
Essence Evolve II-4K - $299 (made the 2020 Stereophile Recommended Components List!
)
Behringer U-PHORIA UMC1820 - $328
M-Audio M-Track Eight - $333
Tascam SERIES 208i - $400
ESI U108 - $470
Presonus Studio 1824C - $500
MOTU Ultralite AVB (I own one) - $649
Zoom TAC-8 - $650
Arturia AudioFuse 8Pre - $799
Steinberg UR824 - $800
Okto Research dac8 Pro - $1160
Motu 1248 - $1495 (I own one)
RME Fireface UFX II
RME Fireface UFX+
Exasound E38 MkII
Merging + Anabis
Focusrite Scarlet 18i20
Focusrite Clarett 8Pre USB
Focusrite Red 4Pre
Steinberg AXR4 - 8 channels of 32 bit/384 kHz
Steinberg UR816C
Lynx Studios Aurora (n)
Digital Audio Denmark AX32 (multi-channel DSD)
Antelope Audio Orion 32HD
Antelope Audio Discrete 8
Antelope Audio Orion Studio Synergy Core
Dangerous Music Convert 8
Mytek 8x192
Merging Hapi
Merging NADAC MC-8
Metric Halo 2882 3d
Metric Halo LIO-8 3d
Burl B16 Mothership
Ferrofish A32 Dante
Slate Digital VRS8
QSC Core 110F
Midas M32C/DL16
Panasonic UB820/UB9000 (UHD Player/HDMI DAC)
OPPO UDP-205 (UHD Player/HDMI DAC)
Can your give an example of a "stereo USB DAC that supports 8 channels?" Seems an oxymoron to me.
The RME Digiface USB has stereo headphone output, but 8 channels of SPDIF. Connect whatever SPDIF DACS you want and they will all be in sync.
RME Digiface USB
miniDSP USBStream B - 8 channels with ADAT
miniDSP UDIO-8
MOTU 8D - 2 SPDIF and 2 AES for 8 digital channels
MOTU 112D
RME Fireface UCX