Hi Greg,
I’ve used low voltage landscaping wire for that type of situation, and it works very well.
It is a direct burial type wire.
I ran mine around the edge of my patio, and covered it with large river rock. (no conduit)
One problem I see with running it with the sprinkler; if a sprinkler head or piping has to be repaired, I’ll bet they damage your speaker wires, when they dig it up.
¾” - Conduit sounds like a nice idea, though I’d still use a water proof wire or the landscaping wire, because chances are 8 out of 10 times the conduit will fill with ground water.
If you’re doing it yourself, and do end up going with conduit, PM me and I’ll tell you what else to watch for.
Regards,
Rick