What you are trying to do is convert the mic signals from analog to digital and route them to the appropriate channels in Logic. The D8 you mentioned has 8 preamps and converts to digital but the output is in ADAT format, which will not connect directly to the Mac. If you plan to send more than one mic signal to each recording channel, you need a mixer.
You need an audio interface in front of the Mac. I use a Delta 1010, which gives you 10 in and 10 out. You can feed each input with a channel or submix from a mixer and then assign it to a track in Logic. On playback, they can be routed through the 10 outputs so you can apply external effects to each channel independently. Look at audio interfaces online (M-Audio, MOTU, etc.) and you'll see what you need and the range of prices. For what you need, the Delta is pretty cheap and they go up from there. Good luck.