does the Mackie Onyx 400f work with Logic on OS 10.6?

Kind of.

Mackie only supports the 400F on Tiger officially but it does work with Snow Leopard. There is a lot of info on Mackie's forums about rolling back the drivers in SL but I did not need to do that and I would recommend doing a clean install of SL rather than an upgrade.

One of the other big issues on Mackie's forum is the stability of long sessions. Some users claim that if they leave iTunes running through the 400F for several hours or even overnight that the audio eventually become grainy and bit crushed. I'm not sold on this test as an adequate measure of the 400Fs compatibility with SL and I've never experienced it with Logic. The workaround, however, is to reset the 400F by switching the sample rate.

The issue I've struggled with most with the 400F and Logic (note: I'm still on 7.2.3) is inconsistent placement of audio on Tiger and a G5 Tower. Basically, the sample offset of recorded audio would vary between sessions so I had to measure the sample offset at the beginning of each session. I've since upgraded to an Intel MacBook and SL and I do less recording of audio and more midi work so I haven't really noticed or cared about this issue. I might be a non-issue at this point.

I hope this is helpful.

Taylor