The LCD has a load status bar, it should tell you how much is left.When booting it seemed to take a while. I assume it was flashing.
Some games will get stuck waiting for the audio section to ping back. That could be your issue if your previous B Board was faulty.I'm not sure what to make of this if the B board will work with that test rom and doesn't with the multi...
I would try to discharge EXC5 again. Also to make sure that it's working properly, is the CPS2 resetting after loading the game?