Is there anything better than saying "Wa Alaikum Assalam Wa Rahmatullahi Wa Barakatuh" to return a greeting, and must the return of the greeting be heard, or is it sufficient to say it to oneself?

The merit of responding to "wa rahmatullahi wa barakatuh" with an addition has been mentioned in some hadiths. Although some of their chains of narration are weak, some scholars believe they are strengthened when combined. It is a condition for returning the greeting of salam that it be audible to the one who initiated the salam.