ION and Mac's

You could try slowing down the dmx speed from the ION in the Settings, Local I/O.  What is the model of the fixtures, we haven't really had any problems working with Mac fixtures.

They are the old Mac 250+ and Mac300's

Questions, 

Your Mac 250s and 300s are in the mode that you have patched on the console.

Your Macs are addressed as patched, Universe/Address@ Chan x

Are you using different universes for your conventionals and MLs, Assuming you are using conventionals?

Are you using the local I/O on the Ion or are you operating some net2 or 3 gateways?

Do you have control of something from the console or are you dead in the water?

Both 300's and the 250's have 3 pin data. So you have 3-->5 pin adapters? and these are correctly put togeather. I don't believe that the 300's or 250's are swapped pin wise. But Could be wrong.

We can start here try to troubleshoot further

Questions, 

Your Mac 250s and 300s are in the mode that you have patched on the console.

Your Macs are addressed as patched, Universe/Address@ Chan x

Are you using different universes for your conventionals and MLs, Assuming you are using conventionals?

Are you using the local I/O on the Ion or are you operating some net2 or 3 gateways?

Do you have control of something from the console or are you dead in the water?

Both 300's and the 250's have 3 pin data. So you have 3-->5 pin adapters? and these are correctly put togeather. I don't believe that the 300's or 250's are swapped pin wise. But Could be wrong.

We can start here try to troubleshoot further