Do Hikvision lower level NVRs (4 or 8 Channel) support recording audio via the ethernet? I know some of the NVRs have a dedicated audio line in.
Do you consider the ds-7600-ni series low-level?
It supports audio recording on every channel, as long as the camera has audio with a supported encoding. Safe bet is to go with Hikvision cameras w/audio, but the manual also gives many third party cameras they claim will work as well. Here is a list of Hikvision cameras that support audio.
Beware of the RCA audio connectors on the NVR, unless something has changed, these cannot be recorded. They are for setting up a door 2-way talkback system.
AFAIK, all Hikvision cameras that support audio, support it via ethernet. The camera line out is for a amp/speaker, which plays the decoded audio stream from the NVR.