MacBook Pro Earphone Jack Impedance when using a Splitter

Hi there.

I'm using an earphone splitter when mixing sound so that I can move between earphones and monitors without having to plug out and in. How does this affect the impedance detection / audio voltage output on my MacBookPro? And more specifically, will the output volume differ for the earphones/monitors when using them with the splitter as opposed to when I'm plugging each in separately without the splitter? When using the splitter, how does the Mac know how to regulate the output?

Regards