I've been on
Zestril, but I don't know about Toprol XL. Since you are under a doctor's care, tell him about your concerns and ask for a trial of an ED medication (Viagra, Levitra, Cialis). I use Apcalis, the Cialis generic, and have been quite pleased with the results.
I don't know what's in Max Stamina that would cause them to put on that kind of warning, but why risk it? Better yet, take the bottle of Max and show it to your pharmacist. He knows best about drug interactions and can give you a knowledgeable opinion.
Here's to putting the lead back in your pencil!