The house I just bought and moved into has a fancy 6-head shower setup
in the master bath. But the water pressure seems completely
insufficient to the task of running more than one head at a time... if
I try to run more, they essentially dribble. I presume that the water
pressure and volume throughput from the well is simply too low. Is
there a product that might help? I was thinking of something along the
lines of a holding tank that could be pressurized and provide the
flowrate needed.

Clearly this is something of a lark, since who really needs a
carwash-like setup for people... it is just a matter of having a
useless bunch of showerheads irking me.

Regards, Teo