I think the first step would be to hook up outputs to the amplifiers and speakers the way you want them to work.
Output format should be set to 2.1, which (hopefully) should work correctly with the UR44. I say "hopefully" because 2.1 as currently setup in JRiver sends a 6 channel signal with three blank channels. That said, I'm pretty sure the UR44 has enough logical outputs even if it doesn't have enough analog outputs, so it should work fine.
The challenge will be finding the correct channel offset in JRiver's ASIO driver options. I have the UR824, but I think it has a different software mixer panel than the UR44. You'll probably just need to keep changing the channel offset until it's correct. It may be right immediately, but if it's not, keep moving the channel offset up one or two at a time until it works correctly.
When you say you want the mains running full-range, but the sub crossed over at 80Hz, do you mean that you want your speakers and sub to overlap below 80Hz? Or do your speakers begin rolling off at or above 80 Hz?
Regardless, you can use the room correction module, or PEQ to set up your bass management/sub crossover. There's a sub option in output format, but, unless you're only going to be listening to 2 channel music, I'd recommend against using that option to create the subwoofer (i.e. it should be set to "silent"). If you're planning for overlap, setting it up in room correction will probably be the easiest thing to do. If your speakers roll off and you're trying to cross in the sub to fill in for that roll off, PEQ would probably be the better option, but I'd need more info about the roll-off you're trying to match before I could suggest specific settings.
Once you've got the frequency setup, you'll need to get your delays set correctly. If you have a measurement microphone (I think you do based on past conversations) it's pretty easy to do once everything else is setup. How you do it will depend on what the transition between the sub and the mains is going to be like, I can outline a few ideas once I know a little more about what the transition band will look like.