Not to be a smart A** but you could always unhook the speaker to the other engines in the lash-up! LOL
LOL, well for that matter I could just turn the volume dial down on the others instead of cracking them open... but I wanted them all to rumble their engines. Boo hoo. : /
I've found that just turning the volume knob down on the trailing engines, but setting the engine sounds all the way up with Reset 6, helps to add realism, whilst keeping the horn down low enough to where it actually makes a bit of an echoed extension from the loudest lead engine horn. Works well enough at least.