How to prepare for a meeting regarding a Ph.D. program I'm wait listed on?
For each faculty member you would be willing to accept as an advisor, know at the abstract level what their recent papers are about.  Search for grants they just received to determine what areas they may be hiring in.  

In the meeting, express enthusiasm for all of these subjects and describe how your background prepares you to work on them.

It sounds like this department has space in only one or a few research groups.  You have no way of knowing which group(s) that is.  If you want to get in, you should market yourself as suitable for as many groups as you can.  It is normal for the openings available to vary by chance and for you to have no information about it; much is left to chance in graduate admissions.