You can be on more than one mood stabilizer tho I don't think that is very common practice. I was on lithium and an anticonvulsant together, along with a few ap's and a benzo..all at the same time. I can say things got quieter in the way of psychosis. The dysphoric mania eventually lessoned. By no means did this combo work for me, in fact I felt way worse off. As far as mixing two anticonvulsants for mood stabilizers I am not sure how that would work. ( ahh I see that was addressed ) Anticonvulsants did nothing to stabilize me, couldn't tell I was taking them at all one way or the other and I tried various ones, seemed like water to me. Thorazine tho kinda of an outdated ap and with not the best reputation actually did help me, but I am not sure how comfortable people are with that one.. including me.
Not that you would react the same as me. But mania with addition of more persistant psychosis like you can see with schizoaffective is more in line with my own experience. Seems like a challenge med wise, at least for me it was. I also have the lovely musical ear syndrome... that can get kinda irritating

specially when you try to sleep.
How do you like risperdal? What else are you taking if anything besides those two?
Do you fund yourself manic often, or do you fall on the depressive side more, or in between?
Sorry for 101 questions, just wondering which meds would seem more helpful to you.