I used a decibel meter on my Marauder some time ago. Around 85 db. I think the problem you'll find with the comparison, is that anyone buying a Maximus isn't going to put a TKO moderator on the end. The gun can be had on the Crosman site for $165, so to put another $100 plus into a moderator doesn't make any sense.
Plus, the US version of the Maximus doesn't have threads for a moderator, so you have to find another way to attach. The Euro version limited to 12 foot pounds is already incredibly quiet, and has threads for a moderator. In that case, the Euro with a TKO would probably be much quieter.
Also, what caliber are you talking about? different calibers, different sound.