I have a gray but she is with the large species birds, not with the little ones. You might have a problem with just a senegal and a gray because the gray will want to be on your shoulder for hours and hours and the senegal will end up attacking it. Sennies are very, very possessive and jealous little birds, Patrick. They are not the 'sharing' kind
Also, you had issues with your senegal, didn't you? Are these solved? Because one of the problems was that you had not allowed her shoulder time so if you now allow the gray to be on your shoulder (and you will have no choice about it because that's what grays love most of all and need to be happy), you will have a royal battle on your hands and two unhappy birds.