As per my understanding you cannot use VirusScan with ENS 10.1. As soon as you will install Endpoint Security Platform, it will uninstall VirusScan.
If you wish to roll out ENS features you can run the Migration Assistant to migrate your existing VSE Policies and Tasks to ENS policies and Tasks.
Once you have done this you should be able to deploy ENS Threat Prevention.
ENS has three core 'modules':
Threat Prevention - This replaces the VSE features
Firewall - This replaces the HIPS features
Web Control - This is the web replutation module which replaces the Site Advisor features.
These are rough comparisons, and the newer ENS products does more and has additional performance improvments. THe ENS core also includes the Data Exchange Layer (DXL) components used by the MQTT protocol to form the common peer-to-peer communicatiosn bus leveraged by TIE (Threat Intelegence Exchange)