Before you dump the da30, remove your MOTU and place it aside, then use the da30 + co adaptor AS your front end into your Mac to check out the results. It then becomes an interface whether tape is in or not.
With all this "gee my old 16bit interface gizmos sound soooooo good" talk around here, you may already own the next coveted 2in, 2out vintage interface right there with your da30.
i've been meaning to connect mine and try it (I have some old fostex cop units that also do optical/coax)... but have been too lazy.
Try it and then report back here how incredible and awsome and mindblowing it sounds. That will help to jack up the resale value for all of our Da30s out here.
"make multitrack sound for long long time"
"I don't understand this shootout. May I borrow your ear canals so that we're on the same page?"
"Lofi is an artform....not a sample rate""