Sony TV RCA output into Yamaha HS80M input via RCA male to XLR male: Is it safe?
Not dangerous at all. You may have impedance matching issues though. And possibly lots of noise in the signal because of the unbalanced source and mis-matched impedance.

Start with the volume on the Yamahas all the way down and, with something playing on the television, nudge the volume up ever so slightly until you can hear the source. You want to make certain a too-hot signal from the TV doesn't rip your speakers apart.

For best results a DI with properly matched inputs for the TV would be my advice. Something like this would do the trick.