You can still use ePO on SBS2011. There's a workaround i've tested on many SBS2011 Servers.
First of all, the important thing is to limit RAM consumption of Exchange 2010.
2nd: Limit the Windows Internal DB to 512MB RAM.
3rd: Limit Sharepoint DB to 128MB RAM.
You can set the limits to any level you want, depending on how many RAM you have available.
I'm in the same situation. We've just purchased another 3 year license after having consulted a McAfee reseller "expert" who in turn consulted McAfee which resulted in a recommendation this was the right product for us (VirusScan Enterprice, MSME and ePO) when migrating to SBS 2011. But now I'm getting stuck in the beginnning of the installer of ePO where it can't find the SQL server ports, and it doesn't help to enable them in firewall. And when I call support then I'm told that SBS 2011 is not a supported product so I can't expect to get support for it. This really sucks!
Is SBS 2011 such a lousy OS that it's impossible to make apps work on it, or what's the problem ? MSME runs on SBS 2011 so why not ePO 4.6 ?