Audio Jack Troubles

I bought the whole PO-10 series this week and the TE sync cable pack but am having trouble making secure connection between the units with each other and my headphones. I cannot fit a standard TRS cable all the way into the audio jack! I have tried to see how far a toothpick would go and it fits to the same length as a TRS cable. When I try with one I get about 4/5ths the way into the jack and am meet with a large amount of resistance. I have tried to push past it but get scared of breaking the units. Has anyone else had these issues? And does anyone know if I’m just being stupid?

If you wanna be extra careful btw, don’t grab the pcb but only the socket while plugging the cable.

@spacestudy. I also just received the PO-10 series. I did not have any problems pushing in the cables so I would think you should be able to get them in with minimal effort. I did have 2 out of the 3 cables that appear to not work correctly though.