Not sure if my terminology is right here so far as Unitrends but...
Last time I tried Unitrends I struggled quite a bit with client throughput with the Windows File Server agent - it seemed to only use a single thread or "reader" process which was just painfully slow, I forget the numbers but backing up a 10TB Windows File Server with 7 million files would have taken pretty much forever.
Has this changed with the more recent versions i.e. can it pull multiple data streams from the same client?