Amp + IEM Question

Hi guys, I've been having a headache trying to figure out if the gear I'm buying will work together, and I'd appreciate your help.

Assuming I have a:

• Roland Cube Street EX (1, 2), with a Microphone and Guitar plugged in, with a 1/4" to XLR cable plugged from the Line Out to a
• Rolls PM50S (1) with a set of headphones

Can I get an in-ear monitor signal from the Cube into the PM50S whilst the Cube is playing? Do I need more gear to do this?

I'm asking this because with my current bedroom amp, if I plug into the headphone port, the amp itself goes silent.

Thanks for your time!