I believe the DRS4D-NXT requires a TZTouch or TZTouch2 MFD.  From Furuno's DRS4D-NXT product page:  The DRS4D-NXT is only compatible with NavNet TZtouch version 4.2.1 or later and NavNet TZtouch2 version 3.0.1 or later

Furuno advertises the DRS4W as the first radar you can use directly from iOS, but, I don't believe this radar has the Doppler capabilities of the DRS4D-NXT.   

Hope that helps

Ben

New Ben is correct all around, I'm pretty sure, but combining Furuno's WiFi radome with the TimeZero iOS app looks interesting:

https://panbo.com/nobeltec-timezero-app-2015-furuno-drs4w-wifi-radar-overlay-more/

I was inquiring about the same thing to Furuno.   From what I can tell the only way to escape the expensive MFD is to connect the NXT radar to Timezero software running on a Windows PC.   This possibility was confirmed to me by Nobeltec and is available since late 2017 and is what I am considering as an alternative as my boat has Navnet vx2 which is not compatible with this radar and I don't want to replace my whole system yet.   The TZ Professional software has the radar module built in and cost about $1400, the TZ Navigator software is cheaper at $500 but you have to purchase the radar module separately for another $500.   Not cheap but cheaper than a new MFD.   

Don, there's discussion of PC TZ with NXT in the comments here...

https://panbo.com/nobeltec-pc-radar-tz-v2-app-blazing-trail-two-ways/

...and I also hear that PC TZ is very good at working with the NXT.