Hi Grumpy_Mike,
The FET route seems possible - but as I'd need 8 (one for each common anode), I'm thinking it would be a bit too expensive. Your project looks great - definitely into the idea of not buying the expensive sparkfun kit. I was thinking about using small sections of glue-gun stick as a diffuser -> where did you source yr acrylic from?
I'm going to try and get hold of an allegro UDN2981A which is another 8-channel darlington array - but this time sources current. Hopefully that'll do it.
(I just need to remember that each one of these dense mistakes is teaching me a lesson... freaking annoying none-the-less)