A bit late, but I have a couple of ideas:
Have the member take and decline a role (you might even create a "role" called Equipment Reservation and then decline the role and leave their request details in the "Please explain why you declined the role" prompt. It should be displayed on the agenda even if the person takes on another role. This might disturb the engagement tracking E-S does, but at least they would have a note on record. It would also let people include details. Multiple people could do this (so all of your speakers who need A/V could have a note).
If you only have 1 or two reserve-able resources, create a role or two titled something like "Equipment: Request Projector" or "Equipment: Request Flipchart"
If someone fills the "role," you know that the equipment is needed. This would prevent the engagement tracker from seeing lots of declined roles" but the drawback is that you'd only know that at least one person needs the equipment, not if there were multiple A/V speeches.