Is it possible to simultaneous run 2 USB DACS to get 4 channels at a single location (e.g. 1 DAC serving Left & Right mains and another DAC servicing Left & Right subs) ?
If so, where might I find the instructions on how to configure this.
TIA
Not with USB DACs, but this does work with some Firewire interfaces, which present a single unified ASIO interface with all the channels from both interfaces aggregated. Most Firewire interfaces are out of software support, though, and there are sometimes bugs in some cases that will never be resolved. For example, the 64-bit version of MC won't work with my pair of Echo Audiofire 8 and 12 interfaces, which present 20 analog channel outputs, plus a number of digital inputs as well. The clock between the two Firewire DACs are synchronized by a wordclock cable.
Most computers don't have Firewire interfaces anymore, but if it's a desktop you can buy a PCIe card. The Firewire interfaces go for pretty cheap on the used market, which is nice if you need a lot of channels. For just 4 channels, you are better off buying a single USB interface that supports 4 channels.
For 2 subwoofers, you aren't going to want 2 separate sub signals. So you really only need 3 DACs. One for L& R, and one for sub. And then split the subwoofer signal into two, and adjust each subwoofer level accordingly, since the sound level will be halved.
Depending on which sub you have, you can also possibly get away with just 2 DACs.
Split the L signal 3 ways, and feed it to the left speaker, and left analog input on each of your subs.
Split the R signal 3 ways, and feed it to the right speaker, and right analog input on each of your subs.
This requires that both of your subs have a pair of RCA analog inputs. Many have only a single LFE input.
And of course in this case, you will lose any bass management features of JRiver MC.