Over the years there have been a lot of misconception about Audyssey in terms of what and how they do things. So I would suggest you start (if not yet) reading up on instructions of how to use it, buy the $20 app, or the $200 app if you want to play around with the target curve. Both can do the job, the $200 app just make it easier, and offers more flexibility. Again, in you research, try to find sites/threads that contain mostly accurate information and posters are more of the objective types especially those that include actually measured results. Can provide some links if you wish... Marantz AVRs at the midrange level are rich in features, many are user adjustable so may as well start reading the Owner's manual too. It's a 326 pages manual that covers just the C50! For comparison, Anthem's that covers their whole 5 models line up has only 70 pages.
Just a side note: If you are in North America, unless you hate the Denon's look, you may want to consider the AVR-X4800H that is more comparable to the Cinema 40, measured very well on the ASR test bench and have additional features that are found on the Cinema 40 but not the 50. For some reason, in Europe the Cineman 50 cost a little more than the AVC-X3800H but in North America, the Cinema 40 50 sells at the same list price as the much better build/equipped AVR-X4800H, making the Denon's a much better value.
The Marantz sound thing is mostly hearsay, originated from their marketing information. Many who have owned both, including me, found that is largely untrue, comparable models sound very much the same as they should due to the use of the same, or virtually the same parts and circuitry (except the HDAMs, only found in Marantz), regardless what Marantz marketing said in their marketing videos.
If you are set on Marantz, and again, especially if you are in Europe, forget what I said about this part. As I said, just a side note.