There are two parts to your question: troubleshooting your current setup and suggestions for something new.
About suggestions for new: directional la, you want to have a computer dedicated only to audio, so no unnecessary programs are running (and if you can make it headless, the better), and an a synch USB DAC. What in particular will be mostly driven by your budget and if you want to stay with Mac.
About suggestions for new: directional la, you want to have a computer dedicated only to audio, so no unnecessary programs are running (and if you can make it headless, the better), and an a synch USB DAC. What in particular will be mostly driven by your budget and if you want to stay with Mac.