Can I connect optical cable to aux 3.5 jack

Sadly Apple got rid of optical audio out a while ago, and replaced it with digital audio out. You would need some kind of adapter.

You can buy an Apple TV, which has HDMI, or a used Apple AirPort Express, which has optical audio out. Either one would preserve digital audio all the way to your AVR or wherever it goes. One advantage is that your MBP would remain unencumbered by cables.

The Apple AirPort Express is readily available on the used market. They are very inexpensive and remain supported by Apple. Just be sure to get the 802.11n "2nd generation" or the original, 802.11n version. They both have optical audio out and support AirPlay audio streaming.

There is an A1264 model on CL in NY for $10.

Do not get the original, 802.11b/g - only A1084 or A1088 model AirPort Express. They are not supported and will not work.

Keeping the signal in its digital form all the way to a DAC is ideal. The McIntosh C1100 has only analog inputs, but that's ok. The AirPort Express's audio output (for example) is a combination optical / analog stereo source. Use a standard 1/8" stereo plug and cable from it to the McIntosh preamp.