Re: UTM Services to High Ends SRXs.

"Starting in Junos OS Release 12.1X46-D10, Sophos antivirus, antispam, and content filtering features are supported on all SRX Series devices."

http://www.juniper.net/techpubs/en_US/junos12.1x46/information-products/topic-collections/release-notes/12.1x46/topic-82931.html#jd0e9420

Note there is no support for Kaspersky av on High End SRXes.