Hello Vic and welcome to the Cow Audio Forum.
I think you'll be fine with the RCA. The line is unbalanced, but try that first. You might want to have the Mackies turned off before you connect them, just to make sure the level coming out of the laptop isn't too loud for them.
Your biggest limitation will be the MacBook output amp. It's at a consumer level (-10). I regularly feed my MacBook laptop headphone out to my Integra 7.1 receiver/amp so I can watch movies from Netflix over the web. I hot plug the two all the time with minimal noise.
Regards,
Ty Ford
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