That's because the 536 doesn't receive NXDN.
Actually, to be technically correct, the x36 scanners do "receive" NXDN, as do most other scanners. They do not decode it, hence why there is no voice. They also received DMR and MOTOTRBO long before the optional upgrades to decode those were even available. And the same with P25.
When I only had one dongle, my 436 assisted me a few times identifying the ota (over the air) channel numbers on some local NXDN systems. Would watch the cc with sdrsharp and scn the rest of the freqs with the 436. I would see the ota on dsd, and see the active freq on the 436.