@ ianlee74 - For my own similar purposes, rather than add transistors to the IO60P, would it not be more [cost] effective to just get a couple of shift registers from radio shack that can be powered separately and source 25ma on each pin? Could the IO60P sink 25ma x 8, instead of sourcing 100ma?
I suppose it depends on the capabilities of the shift register and how you plan to wire it up. For the 8x8 matrix if you’re using a pin for each row & column then you could potentially need 160 mA (8 x 20 mA) per pin if you light all 8 LEDs in the column at once. If you’re going to power it through a shift register it has to also be able to supply this. However, if you’re going to full speed it and light one LED at a time then none of this really matters 
@ Kerbal, Thanks for taking all this time explaining this to me! I don’t know if I’m using the same LED Matrix, but I will give this a try. I’m really new with I2C and shift registers, so this could get fun.
@ IanLee74, Thanks. I’m going to need a lot more transistors :-). I now only use 8 to conditionally set the row ground. This would require 16 more (2x green and 2x red pins). But it would be worth the extra brightness. I will need a larger breadboard as well. And I have to order that rewiring module :-).
Getting this LED Matrix working is a lot more work than I first anticipated 
Transistors are cheap on eBay 
It’s good to have a couple of those in your toolbox. In the meantime, you can do the same thing using a couple Breakout/Extender/MakeBread modules on your breadboard.
In fact, I have a bunch of new Rewire modules laying around here. It’s the Ianlee74 edition v2, now with less solder mask between the holes for easy bridging. I’ll get them up on the store here soon.