No, it's not necessary to have another product if the SOHO product already features a virus and firewall protection module. Theoretically, the antivirus protection should be able to detect any possible malware attempts.
If you have a powerful computer, install Malwarebytes Anti-Malware as a dedicated solution for malware infections.
Malwarebytes: http://malwarebytes-anti-malware.software.informer.com/