Downdraft vents won't move enough air to clear the heat off a commercial style 6 burner. A remote blower and an overhead hood are the best option for the 700-1100 CFM you need to exhaust with these ranges. I've done inline remote blowers and wall or roof top remote blowers and blowers right in the hood. The farther the blower from the hood, the quieter it will be...and the less effective. Hood and range manufacturer's have specifications that you need to take into account. The specifications for the CFM (cubic feet per minute) for exhaust air and calculations for duct length are available from the manufacturer's websites. We have installed almost all the major manufacturer's commercial style ranges (and some not so major). We select a hood that fits the range specs at the same time, whether it is manufacturer's stock or a custom hood with a liner and blower unit. I'm not in the brand rating business...I don't get call backs on most appliances...maybe check out the kitchen appliance issue of Consumer Reports for ratings..I heard it just came out recently. They usually have it at the local library.