This may well be a driver problem, but I'll ask anyway:
I have a Delta 1010. I can set it up in AMS. When it is detected, and I click on it and look at the advanced settings, none of the receive or transmit channels are colored in. I select them all, and exit and all is good. I can then add instruments, and draw cables to them. Again, I can exit and come back, and it is all there.
Then I play with Metro for a while, after making the midi setup reflect the AMS document from the Outputs and Busses section. Sometimes this works, and sometimes it does not bring the settings in. At this point things get fuzzy and I am not sure what is causing what, but the cables are gone from the AMS page, and the RX and TX channels are gone again. Usually I have to restart Metro with the AMS page open, reassign the midi setup, and it doesn't always take the first time.
I am using the latest Metro (6.103) and the latest Delta 1010 drivers from Midiman. This is on a Dual 1.25 G4 with OS X 10.2.8.