bass amp with organ pedals?

I have a conn 645 theatre organ(look it up) im thinking of buying an
bass amp for. im a classical organist, and my pedals dont sound right
because i have to use the 16ft tuba voice to be heard with the manuals
but it makes it sound horrid/cheezy (for classical at least). if I
dont use the tuba, it sounds well, but its not loud enough. so im
thinking of buying it an amp so i can directly control how loud the
pedal voices are, so i dont use the tuba. So the question is how can i
connect the amp to the organ and only have the pedal voices speak
through it?and is it possible to have the pedal voices speak through
the organs speakers AND the amp? Also, is there other ways to make
the pedals louder other than the 'pedal-level' box inside the organ
so maybe dont have to buy an amp?