I'm successfully get this Asus U3100 Mini plus DVB-T working under linux (18.104.22.168) after horrible 2 days code breaking :). In fact, these steps here are almost correct, but there must be some more code correction to working well.
1. in file af903x-devices.c line with .num_adapters = 1, needs to change to 2
2. in file af903x-drv.c on 3 lines here is calling function: DL_SetBusTuner there must be hardcoded Tuner_FCI_FC2580 error = DL_SetBusTuner (PDC, Bus_USB, Tuner_FCI_FC2580);
-- and it is good to eliminate all warnings by compilation.
I don't know exactly if it will be enough because I changed many other lines in code and I don't remebmer all this changes. I try later to generate some diff file. If You are still interested in this topic I can post here some patch for more comfortable installation. Thanks for your "howto", it's good to see my favorite TV on my VLC in linux destktop :)