I represent Sound Research MIDI products.  Knowing that some devices
need more current than the .5 ampere  driver of the ULN2803, I provide
outboard drivers in groups of 32.  These come as Darlington
transistors, or FETs, relays or triacs.  The package size is 6" x 12"
x 1-1.5", depending on output device.  My relay coils use far less
current than most solenoids.

Take a look at http://www.Sound-Research.net/ to see if one of my
driver setups will take care of your situation.

Vern Jones, Sound Research