The issues involving having 2 of something--whether it is antivirus apps or
firewalls, are somewhat overstated and probably oversimplified. I've seen
both done without significant problems, although 2 firewalls are more likely
to lead to difficulties than 2 antivirus apps, from what I've seen--not in
terms of protection, but in terms of understanding what is
happening--clarity of alert messages.
But to answer the question--I don't know! I don't think I've seen
first-hand a machine running the Security Center and two antivirus apps.
Anybody else know?
--