The stock Velvet.apk is removed in custom ROM. You need the original one in system/priv-app. Then do the update to the latest from Play Store. It should work.
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Uninstall your current Google Now/Search then flash the attached Velvet.zip in recovery. Reboot then update to the latest from Play Store ... that's it.
Open google now - settings - enable google now
Select Voice - Language set to English (US)
Audio History - On
"Ok Google" Detection - select what you need