While there are plenty of stereo stand alone usb DACs out there to get computer audio library's stereo music to a receiver, integrated amp, or preamp, which does not have an internal DAC, I have not seen any external DACs which accomodate multi-channel music I have on my computer
I have used a computer exclusively for music/movies since 1991 and have had multichannel DAC's since the M-Audio Revolution 7.1 soundcard. There are many current ways to utilize a multi-channel DAC with the PC. I've used AES3 (also calledAES/EBU),ADAT Lightpipe, Firewire, MADI, USB, AVB (via ethernet),Dante (via ethernet), Thunderbolt, HDMI, and DisplayPort. The best multi-channel DAC I've used and what I would recommend is the MOTU 1248 with Thunderbolt. I also own the MOTU 624 and Ultralite AVB.
The Motu 1248 is best with a PC for many reasons:
Web App Support - The control software (mixer, routing, settings) for the Motu is a web app located on the audio device. Any browser on any web client platform can access the software. You can use your phone, tablet, or computer to access the software and make changes or see what is going on.
Routing - Any input can be routed to any output. This makes it easy to setup ASIO channels the way you want. This has valuable considerations for multi-zone output.
12 balanced outputs - There are two output labeled "Main", two outputs labeled "Monitor", and eight labeled "Analog Out." You can route up to 64 channels out through ASIO and can assign any ASIO outputs to any of these 12 physical outputs.
2 headphone outputs - Like any of the Motu outputs, these can be assigned whatever channels you want. If you want the headphones to get the same output as Left and Right speakers, you can do that. If two people want to listen to different playlists on two Zones in JRiver Media Center, then each headphone output can be assigned to a different Zone.
ESS Sabre32 Ultra DAC converters - high SNR and 32 bit output means volume control is completely transparent, excellent sound quality. Your media player should be set to dither to 32 bits rather than 24 bits.
Low Noise Floor - With the ear up to the tweeter and nothing playing I hear no noise at all. Some audio devices will have a hiss that can be annoying with higher sensitivity speakers.
No noise on sample rate changes - Sample rate changes are completely silent! No slight tick, pop, or anything else. This is perfect for home use when listing to a playlist of mixed sample rates.
No noise during on/off when amps are on - You can turn the Motu 1248 on/off and never get any noise out of the amps - no tick, pop, click!
Multi-client ASIO driver - This is a huge feature! With most ASIO devices including my 16 channel Lynx Aurora 16TB, you can only use one instance of the ASIO driver. With the Lynx, if eight channels are in use then you can use the other 10 channels for other Zones. With the Motu, it is truly multi-client. You can access channels 1-8 for a home theater and use the other channels, simultaneously, for output to other Zones. You can also access the headphone output Zones the same time as the other Zones and even use both headphone outputs simultaneously with different content.
DC Coupled Output - With no capacitors in the signal chain, there is no rolloff or phase shift of the low frequencies.
+20 dBu line output max level - The maximum level out I've seen of any DAC is +24 dBu (Lynx Aurora VT, Solid State Logic Alpha Link). You can compare the maximum output to get an idea of maximum volume differences among DACs. For example, the Behringer Firepower FCA1616 has a maximum output of +8 dBu and the Steinberg UR824 has a maximum output of +18 dBu. The Motu can output 12 dB more volume than the Behringer and 2 dB than the Steinberg. This is helpful when using EQ or convolution because this DSP always lowers the output signal.
Output Trim range of 24 dBu (+20 dBu down to -4 dBu) - Even though the maximum output is 20 dBu, you can lower the maximum output level on each channel using 32-bit digital trim levels. This is helpful if matching speakers or amps with different sensitivities. You can also use it to make sure you don't ever overload the input on a small amp used on one of your Zones.
Mic with phantom power and line inputs - To do room measurements using software such as Room Equalization Wizard (REW),you can just connect a microphone, push the +48v phanton power buttom, and start measuring. No extra mic preamp is necessary. If you have an Earthworks M30BX microphone, with built in preamp, you can connect it to the line input without having to go through the preamp section. The Mic and line inputs also let one play other instruments such as a keyboard along with music and even do karaoke with up to 4 microphones.
Guitar inputs - These probably aren't helpful to most, but it does let one connect an electric guitar or bass and play through their system along with the music.
Auto-sensing mic inputs - If you put a TRS jack into the mic input, it will disable the phantom power option. You can only use XLR jacks for the phantom power to be available. This prevents you from accidentally damaging equipment.
Thunderbolt connectivity - You can connect with Thunderbolt and get about half the latency of USB.
Variable USB buffer and ASIO buffer - You can change the USB buffer using 5-6 different settings from Lowest Latency all the way to Safe. You can also change the ASIO buffer size.
AVB Network - You can connect a 2nd device using the ethernet jack or 5 interfaces using the AVB hub to increase channel counts. There may be 2 channel AVB compatible devices in the future that would let you easily add Zones that are always in sync.
