LED # in dreamcast?

[Macabre]

Hi guys! Random question about the number of possible leds I can stuff in a dreamcast. I know of the ground, 3.3, 5, and 12 volt points on the power board, and I have a nice pile of 5mm leds, each with a built in resistor. What's the best way to wire these up? Would connecting each to the 5v and grnd point be the most effective, or would it be ok to put 2 in a row and connect them to the 12?

Any help here would be great, the most I've done with leds are simple stock power led swap outs!