Is the Sunsynk SYNK-SG01LP1-(Max) SYNK-16K-SG01LP1 (Max) compatible with the Sunsynk CHNT DDSU666 (1ph 80A)?

Yes — listed by the manufacturer.

The manufacturer's published pairing data lists these together.

▦Manufacturer's compatibility listListed together in the manufacturer's published pairing data. A cited document reference is being added as datasheets are processed.