I just read that toroidal transformers are a lighter kind of transformer that you can put in your amp. Is this true? Can I get rid of that super heavy transformer and replace it with a lighter toroidal one?
You are talking about the power transformer I assume. Yes, that is correct - as long as you can find one of the correct voltage and current ratings. Toroidals rock. If they weren't so expensive nobody would use anything else.
you can ask your local amp tech if your amp can fit one.