that's good news!
i was wondering about the brightness of the leds - i can imagine that if you light a single led it's fine, but they must have become dimmer and dimmer the more leds you want to light per column.
just to satisfy my own curiosity, i ran a small simulation (because it's easier than math. hah.)
i treated the current driver and sink IC's as near-zero resistors. that is: i ignored them.
a 5v power source with single standard red led and 270R resistor yields about 12mA of current. which is great for a single led.
two leds in parallel, joined at the single resistor, have to SHARE that current. that makes for 6mA per led.
3 leds run at 4mA, etc, you get the idea.
so 8 leds run at 1.5mA each. no wonder they were too dim..
now scaling the voltage up to 9v, total current is just over 26mA.
meaning: LEDs would be a magnitude brighter.
however, if you only light a single LED, it gets the full 26mA. standard max current is said to be about 20mA, and leds will usually survive short peaks up to 30mA. but still - danger zone.
the only way to avoid that physically is to give each LED its own dedicated resistor, and parallel all those combo's.
however, with off-the-shelf led matrices you don't have that option.. hmm. google!
from what i gather from info on the net, is that differences in brightness (1 led/column vs 8 leds on at the same time) are usually countered digitally by adjusting the PWM in the program you're running.
don't know if that's of any use to you, but i did learn something new