Well yes you can, but your options are very limited and you need to be ready to spend some $$$
The Mytek Stereo 192DSD has an option in which you can stack three DACs with a USB hub. This would be a 5.1 solution only. The driver takes care of assigning which channels goes to which DACs. Just like you asked for. They are $1500 each, not taking into consideration the usb hub. But its a well regarded DAC in its own right and its very versatile. A link with a Demo using JRiver is here at the Mytek homepage:
http://mytekdigital.com/hifiYour other options are from ExaSound. Either the e18 or E28. Both are 8ch multichannel DACs. The e18 is multichannel PCM only and DSD stereo, while the e28 does multichannel PCM and DSD. The e18 is $2500 and the e28 starts at $ 3,299.
If you are serious about this, I would recommend the e28. Look for reviews of the units, I would love to have one.
hope this helps