Hi Vicon
Apple is changing many of the underlying frameworks and associated APIs for audio and video. El Capitan introduced many changes and broke lots of hardware/software for audio interfaces and software.
Most interfaces depend on "drivers" to function. Not sure about iMic. You will need to go to Apogee's website and see if new drivers exist and if they are still supporting that device. Sorry to say, my closet has many outdated, no longer supported devices. Even my current Focusrite 18i20 has had some issues and I don't think Focusrite has updated the Mix Control software yet.
Some of the older USB devices depended on using built-in Core Audio device support and with El Capitan, these got flakey to say the least.
AFIK Jack Router OS X has not been updated since 2013/14 and most likely is not compatible.
Many other free routing software also broke like SoundFlower. There is a new version of SF 2.0.2b2 that partially fixes SF and the original developer has taken over development again so a new version is in the works. Rogue Amoeba was maintaining SF for many years, but they decided to drop free apps. They have some commercial apps that may provide you a working interface. I have not use them, so try before you buy https://rogueamoeba.com/
One app to check out by them is Loop Back
One thing to try is using GarageBand to see if it would work.
The next thing I would suggest is to create a bootable external drive (ssd is preferred) with Yosemite or Mavericks installed just for recording.
It is possible that solutions will be coming in the future, but it is already pretty late in the game of EC so I assume if the developers/manufactures were planning on updating, they would have. It is always best to make sure all of your devices and software is compatible before upgrading OS.
It is up to the developers/manufacture's to provide this support, NOT Apple.
Sorry I can't help more.
Greg