I would really urge you to get a decent audio interface for this kind of work.
The regular iMac output is okay, but not aimed at professional audio and really only designed for people to listen to face time and mp3’s.
You might also experience less cpu use when using a good audio interface with well written drivers, which most are these days.
There is steinberg’s own range of interfaces, and popular among many users are the Universal Audio interfaces that connect via thunderbolt, have some of the best preamps in the business and also offer onboard DSP for emulation of vintage hardware equipment as realtime plugins you can use in your sessions.
Cheers,
Joe