Well, i have some results.
Hyo's 167000 worth army (a bit too much) on VH. I made the Arcani a general unit, so that he is nigh impossible to kill early. (a slight difficulty increase)

Against my bulls/slingers

At Alpine Valley battlefield (where i start on the bottom..)

Result 1 (Proper attempt, no exploiting of AI dumbness.). I sticked to the left side, as there was a slight elevation, allowing my slingers to inflict some more damage. Made a few mistakes and so we lost. (chain rout when my general died)

I think it's doable, but would require a perfect plan (or exploiting AI tunnelvision, but we don't do that!) Overall it's far too strong army for Spanish 50k, due to nigh unbreakable morale.
Oh well. There, you can celebrate now

Overall the battle plan was sending my generals out, to split some roman cav, and gangbang on them with the generals, 4 fanatics and slinger fire. While Bulls were in a 2,5 line formation (2 lines mostly, 3 at some points) The fanatics have proven to be too weak against 9/3/3 Praetorians, and could only temporary rout them, with heavy loses.
The main battle was going nicely, but when fanatics and generals were finally slaughtered, the wave of fresh enemies turned the tide of battle, and so we lost our general.. After his death, every infantry flag turned white.
Our loses would be lower (despite the defeat) but one unit of slingers was standing unattacked for two minutes, allowing Romans to kill 1000+ fleeing Spaniards.
Perhaps there is a better way to organize the troops, and thus win, but i didn't come up with one

I just noticed, that it was Hyo and not Barbarossa who made this army. my bad!