I have your same problem but have no option to enlarge the vent duct due to the size of the space between the wall and ceiling studs. My previous vent hood was a 36" Cavaliere 900 cfm for a 36" Dacor Epicure cooktop. My new range is 36" DCS with 6 burners. Because I wanted a more substantial look, and after much searching and debating, I bought an AirPro 860 cfm (link below) The Cavaliere hood was more than what I needed for the 36" Dacor. I never turned it up past 1 or 2 while cooking. On 6, the highest speed, it was kinda loud but since I never used it on high it wasn't a problem. The AirPro has not been installed yet so I don't know what the actual noise level will be but it's rated at 35 / 0.7 to 67 / 6.5 (Lowest to Highest Speed). I just couldn't see paying thousands of dollars for a vent hood especially since my $400 Cavaliere had worked fine for 5 years. During my hood research one of the retailers did tell me there was a vent outlet adapter available online but because our contractor wasn't thrilled with that idea, I stayed with the 6" hood duct. Hope this helps. Good luck in your search for the right hood. Here is a link that might be useful: AirPro Hood

You may be better off asking this over on the Appliances forum. But you'll probably get a lot of differing opinions. This old thread is probably a good place to start, especially if noise level is a major concern for your setup. The consensus there seems to be that Vent-a-Hoods are fairly noisy, and some people say they're also hard to clean. Laura

Do you have a budget? I ask because there are a lot of things out there but they vary in price. For a range like the NXR you want at least 600 CFM. You also want to look at how you clean the hood. I shied away from the vent-a-hood because some reviews indicated they were difficult to clean.

It is unclear to me whether you would need a custom hood or not. ModernAire is one possible source. Before that, however, please read the hood material on this forum for understanding of the requirements for good ventilation. Requirements precede the ventilation system parameters that can achieve them.