I haven't used mine for a couple of years now, but I have a Behringer FCB1010 midi foot pedal, and I used to use it with Guitar Rig 4. I do not know if you have some different model or not, but if it is the same one, then I think I might be able to assist.
I will try to find some notes I think I have somewhere on what I did to get it to play nicely with Guitar Rig, and those should apply to using it with TH2, as well.
There was nothing at all special that I had to do, as far as 'order' goes. It is simply a midi device device to Sonar, so just make sure you have the connected port enabled. I used to plug mine into an E-MU X-Board 61, but it doesn't matter, as any midi port will work. There should be nothing to do in your A-300 whatsoever, as it will just pass data to Sonar (to the best of my knowledge. I did not have to do anything with the E-MU when it had the pedal plugged into it.)
Here is a link to the Yahoo User Group for the FCB1010:
https://groups.yahoo.com/neo/groups/fcb1010/info In the above, there are a bunch of 'how to' posts for configuring and using the pedal for controlling software, as well as setting things up on the pedal itself.
I hope this helps - I will be looking for my notes, and if I find them, I will circle back and post them here.
Bob Bone