No one in life likes to feel they are getting an inferior service compared to others. This is especially true of virtual event participants, dialling in to a live event.
So avoid ‘side conversations’ in the plenary room that they probably can’t hear and will definitely feel excluded by. And remind yourself they are there by turning laptops with their images on, to face you, on every table. That way they have a presence like every other participant, and will be front of mind, as you deliver a first class service for everyone.