Ah, you can't that I'm aware of. There are no insert points on the BR's. They are an all in the box solution. The only way I'm aware of that you could possibly do it is to export the .wav or burn it to a cd then hitch the 3630 up to the playback device (not the BR) and record it back into the BR to that way.
But I wouldn't bother. There's enough effects, compression and mastering options inside the BR1600 not to worry too much about external devices I'd've thought. Especially given that they are only 16bit 44.1kHz machines.
And, that you can't patch external devices to them anyway.
But who knows, someone out there may have achieved it somehow.