Im missing the purpose. Are yall saying you dont just use good silicone wirenuts and good 3m tape for making landscape speaker connections? Thats all I use and its never been a problem. Why go thru all the added work/expensive when using what was designed works just fine? Yup, Im not getting this. Talking about something more than speaker connections?

What part of the country? If you don't have to deal with snow, sub-zero temps and wire-eating critters, consider yourself very lucky.

Right on the bag it says "Maximum 30 Volts"! Probably not made for a 70 volt audio system.

In this famously damp part of the world, the only way I would dream of doing this for a permanent installation at or below ground level would be with a resin joint. Use whatever your preferred above-ground connection method is and then set it in a block of resin inside a suitable box. The size and shape of the box may depend on what angle you want between the cables you are joining. Often, this is sold as a kit around here, sometimes including an enclosure or connector that I don't use. For example:
[Link: screwfix.com]
[Link: swaonline.co.uk]

TTTT,
Fascinating.
I wonder what they use on the frozen tundra.
I understand that in Tahiti they don't build wood-constructed buildings with cover on both sides of the wall, as the stuff that grows inside closed walls is nasty indeed.

Local conditions.

Not sure if this would work for your application, but in the past when I needed to splice wires underground this is what I have done. Cut a sort piece of conduit, slide over the wire, splice together. Slide conduit over connection and fill both ends with silicone. Not something you can access or work on easily, but never had a connection fail and some are still going 20 years later.

+1