Disklavier

Hello everyone
Until recently I had my DKC850 (which runs a mpx1 piano) connected via ethernet cable to my iMac and  worked well. I am now in the process of changing internet provider and at this time I have not anymore a "box" which was the internet connection port, and I have change my Imac for a new generation one... and whatever way I try I cannot make a connection between the DKC850 and the iMac... Therefor I ask here for some help.

The old configuration was hooked up this way:

DKC850--> DLink Router
Imac-----> DLink Router
Internet box-> DLink Router

I do not remember how I the settings were made... maybe automatically the imac recognized the DKC850 or maybe through the web page of the settings of the internet box...
Anyway at this point now that box is not there so how to configure?

Do I have to enter something under the "network" menu of the DKC850 or in the network tab of the preferences of the iMac (I try with the router but also directly bypassung the router) ?

If so what do I have to enter and where ? The protocol selected actually is DHCP but I have tried all kind of other settings with no results. I thought the Imac would detect the DKC850 but no...

Thanks for your assistance !