I did the same thing, purchased a new remote from ebay. When I called the number on the Karr Security website they asked me where I got the new remote. I told them ebay and the guy over the phone was a real jerk and basically told me that he knew how to program the new remote to the alarm but would not tell me since we did not purchase the remote form them....
Sorry for the rant but you can imagine my frustration.
Well I was able to find a process here on this site but cannot seem to find the thread.
But the way that I added a new remote to the Karr 2040 was to
1.open car door
2.turn key to "ON" position
3.press valet button 3 times
4.Now the car is ready to recieve new signal from new remotes. Press and hold remote button #1 until you hear a chirp. I was able to add 2 remotes this way, however we went through the process of turning the car off then on for the 2nd remote.
Not sure if there are additional channels that you could add but we have 3 remotes total now.
I will keep looking for the post with the real steps but this method should work since it worked for me.