hifi engine

Recent proud owner of the Rotel RA-412

Having a brief exploration of the unit and testing with Headphones I've discovered the Right input channel for Aux is distorting and lacking power, however does not seem to be a problem via the Tuner input. Is this likely to be a matter for soldering or replacing of parts?

I don't think I'll be using particularly large speakers with it at this stage but I am curious about bi-wiring and whether hooking up a cone per speaker terminal is likely to produce any real benefit/ not kill the fuse?

Any help and info greatly appreciated.
Many thanks