Here is what I have dug up on RT_Socket, I don't know wat PS Combo is either... this forum is monitored by an AE Services SME.
The RT Socket interface is implemented by Reggie Slavens (rslavens@avaya.com) with Avaya Professional Services (i.e., installed and configured by APS on CMS). Reggie can provide a DevConnect member the lastest technical specifications for RT Socket, which would cover the (agent, VDN, and skill) data items provided by the generic interface. The member can then determine whether the generic interface is sufficient for their solution. If not, they can discuss customizations, which APS would address. Historical data is handled by someone else in APS whom Reggie can put you in contact with if you wish.
The following document lists the data items available in CMS, Avaya CMS Database Items and Calculations, located at
http://support.avaya.com/css/P8/documents/100114786
Another option would be to use ODBC and JDBC,
http://support.avaya.com/css/P8/documents/100120763. In this case, APS is not involved.
You now know more than I on this topic. Good Luck!
John