Map updates off, but hydrophone lines on

Okay, I've found a solution and will post it here in case someone else wants to know.

It seems that TDW's add-on mod has a version called "No contact shapes or colours" which essentially removes ship and aircraft symbols from the navmap, but leaves hydrophone lines (although it also seems to remove the color from hydrophone lines, I hoped it wouldn't do that). You have to have Map contact updates set to ON, to see hydrophone lines.