The upgrade does not include NXDN, but it does make it a better scanner. It does not have enough ROMmemory to handle both DMR and NXDN. I have a Pro 18 and a PSR 800 and the upgrade not only adds features but also qualifies it for factory service if needed in the future.
GO to the pro-668 facebook group and the file section has a copy of the original microsd card with all the files for a stock RAdioSHack Firmware pro-668 including iscan. https://www.facebook.com/groups/809759642433559/
The best thing you can do to fix it is the legacy upgrade combined with a better antenna and a name brand Micro sd card.