Does your mic require phantom power? There are lots of ways to get an XLR mic into a Mac. A mixer that powers the mic and then feeds a digital signal (Optical SPDIF) is one. A converter to firewire or USB is another. Metric Halo, M Box are examples of this.
If you have a card like a Kona, Matrox, MOTU, Decklink some versions of these cards have digital and analog line level inputs so a mic preamp with analog line or digital outputs can be patched in that way.
Personaly I never use the VO tool. I have Fairlight so it is better to do VO recording in a dedicated DAW. Many people prefer Sound Track pro for VO record.