Dinner after Pumpkins
There are several places close to the Auditorium (easily walkable), but not the ones you mention. Custom House is nearby but it sounds like you're looking for something not as pricy (and may not be open late enough). Edwardo's on Dearborn has "stuffed" deep-dish "stuffed" pizza. Hackney's on Dearborn has burgers, "French dip" roast beef sandwiches, and their amazing onion loaf. Exchequer Pub and Miller's Pub on Wabash are two long-time pub type places serving ribs, burgers, pizza, etc. Mercat a la Planxa is near there for tapas-type food. All of these places are within a five-minute walk (roughly 1/4 mile or so).
Regarding the wait at Avec, you didn't mention what day of the week. If it's a Friday or especially Saturday night, it could be very long. Other days of the week, it's not bad at all.