Does your new iMac have Thunderbolt 3 (USB C) ports or Thunderbolt 2 which is backwards compatible to TB1?
Check the specs of your iMac before you order any adapters.
You connect your FW400 cable from the Duet to the adapters to connect to your iMac.
In my case, I'm able to connect a FW800 cable from a MOTU Track 16 to a FW800 to TB2 adapter which is connected to a TB2 to TB3 adapter which connects to a 2017 MacBook Pro which has TB3 (USB C) ports.
Ok...$85 and two apple adapters later I now have Duet as my default sound source again, however when I open Maestro II no Apogee system is recognized. In other words I have no control of inputs and output. Has anyone else encountered this problem?
Maestro 2 version 2.8.8
Well...I tried a reinstall..no go so I went to the apogee support page requested a software download. HIgh Sierra is "not tested." Evidently that's a compatibility issue and the reason for their buy back program. As a songwriter/musician with a small home studio I don't really feel that I need to be married to Apogee after this.
I traded my FW Ensemble after the release of OSX Lion, OSX 10.7 as Apogee, a company dedicated to Apple, did not have their drivers updated. At that point I had to use my venerable MOTU 828 MKll which worked like a champ.
I apologize for not following up earlier but I've been under the weather.
After much debate and hassle I finally broke down and purchased an Apollo Twin. I'm pissed at Apogee but I'm even more pissed at Apple. We are herded like helpless sheep from one upgrade/expenditure to another. As I have posted among friends on FB; buying into to Apple is like stepping on fly paper....you're stuck for life. Simply because I needed to replace an old computer I've now had to invest over $2000 to get back to where I was. Thanks to everyone for your help