Since it has ADAT output/input, you could connect two of these for 16 channels of balanced output.
I've never heard of an ASIO driver that didn't access all of the outputs. I'm sure this will work fine with JRiver for 8 channels of output with one and 16 channels if you add a second one.
I haven't heard of an ASIO driver that didn't reach all channels either, but someone in the thread over at Gearslutz asked the Behringer rep if you could slave it to another interface via ADAT, and the rep initially said that it couldn't be done, but later seemed to backtrack a bit (saying it could be done if both interfaces were connected to the computer), but said it wasn't supported/recommended.
The issue seems to be the lack of mixer support (i.e. the ADAT ins don't automatically go out the analog outs and can't be configured to do so in a "set and forget" way), so the Behringer needs to be connected to the PC even if it's the slave, and channel routing needs to be done in software.
All that made me wonder what other limitations it might have, or whether the Behringer team is just confused about their own product.