I dunno what but that nsx obviously has other mods that is making it sound that loud. There are clips of gruppe m on the exhaust clip thread and ppl should listen to it if they want to know what it would actually sound like on a stock nsx if they're considering the exhaust.
Thats Alex V.'s car from Gruppe M USA. He has this exhaust on it now
http://daliracing.com/v666-5/catalog/index_browse_part.cfm?focus=1718
His car has the Gruppe M Supercharger, Intake, Exhaust, Headers, BBK, JRZ suspension, Gruppe M everything basically and a lot of custom or upgraded stuff. His internals are all stock from what I understand.
His car sounds mean with the Ver. 2..... I can't imagine with the Ver 3