You should be able to change the codec/format in the ventrilo_srv.ini file. Halprin made a post here that explains the various information about each codec:
http://www.ventrilo.com/forums/archive/ ... -9540.html
As for the clients, it's hard coded at 8 for the public version of the server. If you wan't to go any higher, you have to rent a server from a 'licensed' provider -- see
http://www.ventrilo.com/forums/archive/ ... -7322.html for more info. But if you were a licensed provider, you would be able to set the max clients with a variable in the ventrilo_srv.ini file.