last week we successfully tried zita-njbridge to get a high quality
audio link between Norway and Germany. No audible dropouts, however, the
round trip latency without the sound cards 72 ms (measured with jdelay),
which was too much for a satisfactory jam session. We used the default
settings of zita-njbridge, no buffer tweaking, 24 bits/sample, 2
channels.

The manpage of zita-njbridge says it is for local network afaik

Might as well mention that I'm using Mumble and uMurmur with opus as a temporary STL for a radio station and getting fairly good latency.   1.3.0 has built in jack support. 

-Sam