Yeah you can add talkgroups. Just be advised, there is a bunch of talkgroups in the Special Group that can be removed, if you get close to the 200 talkgroup limit per system.
From your location I dont think you will be able to receive the airport talkgroups. They are on another control channel. This one is not simulcasted to all of the other towers. Site 103 -
http://www.radioreference.com/apps/db/?sid=2508.
You can try unlocking the other frequencys. But the way this system is setup. There is only 1 control channel that carrys all of the PD traffic all of the time. 867.2125 which rotates with 867.9625. The others in the list are on a tower way over on the westside.
There have been problems from people claiming broken up and choppy recieving. Usually it boils down to an interference problem with a surrounding tower simlucasting on the same frequency--but being recieved a a slight delay. Search back a couple pages in this forum for more on this problem.
The solution is usually some type of roof mounted anntenna.
The files I sent are what I use without issues, and I hear every active talkgroup for Phx PD/MSCO/etc. They might not be exactly what you are looking for, but it should help get you started..
This system is somewhat complicated. Do some searching in this forum and you will see what I mean.