Not that it's any help but I get this problem with my Bravia to PS3 using a authorised sony optical cable.
So all Sony stuff and none of it fits
My solution was electrical tape as once they're in, they work fine but they slide out at the slightest vibration so the tape solves the issue.
Intel Core i7-4790K 4.00GHz - 32GB Kingston HyperX - Gigabyte Z97X-Gaming 7 - EVGA GTX 980 TI SC 6GB - Asus ROG Swift PG278Q