I think your math is a little off and the terminology can get confusing as mentioned. If you have 32 strands of 100 pixels, then yes you will have 9600 channels (not RGB's) and a universe can address at most 512 channels. So to address 9600 channels you will need at least 19 universes. I don't know if you changed anything from your screenshot. In your first screenshot on the layout tab, you have the Megatree set up correctly. In the second screenshot on the Set Up tab, you only have Universes 14-22 set up for the controller. You need universes 14-32 set up for that tree. You can combine more than one strand on a controller port. You might expand in the future and it is nice if you leave yourself some room so that you don't have to redesign things when (not if, LOL) you do. Depending on your set up, one port can handle over 1000 pixels, but I wouldn't push things to that extreme. I would also suggest letting XLights do a majority of the work for you. There are several methods and ideas on how things should be set up and they all work. Just find one that works for you. I set up my Universes to start at 100, 200, 300 etc. and each controller will start on one of those series of Universes and only set up as many "100 series" universes as I need. In Xlights, just setup the first model that you are going to connect to that controller as the Universe number and Channel 1. Then each model after that you will tell XLights to start after the previous one and it looks like you did that with your Megatree star. That way, Xlights will keep track of Universe assignments for you. If you set up the controller connection in Xlights, then you can use XLights to upload all the information on your show to your controllers so that you don't have to. Makes life much simpler and makes expansion in the future a little easier as well.
After you decide on the design of your megatree and how many ports you are going to use for the controller,then enter the number of ports you are going to use as the number of strings in the Megatree model. I would suggest using 8 but you could use 32,16, or even 4, but that might be pushing it. I would suggest setting up the controller connection and pixel protocol in the models info and then XLights can set up your controller. And if you make any changes in models, or design, then you only have to make the changes in XLights and then re-upload your controller information. No need to go to the controllers and keep track of all of the universes and port connections. And as allknowing2012 mentioned, try to avoid Multicast if you can. I hope I didn't make the muddy water muddier! Let us know if you need any more information.
