With regards to fallback tuner and bouquets. The box in use has its own bouquets. You either import them, create them or use a plugin to create them. Fallback tuner does not do anything with importing bouquets. If no tuners on box, it falls back to a remote tuner.
Remote Stream converter plugin allows you to import bouquets from another receiver.
I am afraid I don't know too much about client mode, so can't help. There are a few people on forum who use it extensively, I'm sure they will post in the thread.