Can anyone tell me what the dual conversion 5 channel reciever from FMA can do if I use it with a 7-9 channel reciever?

If what you mean is 'what you can do with it when used with a 7 to 9 channel Tx' then you will still have five channels of operation but no more.

By explaining what it is that you want to do then you would probably get a better response.
John