The MOH input is usually 600 ohms (unless you have a 600/8 ohm switch) and the line output of a radio or CD player is 8 ohms.
If you can make it sound good enough without a transformer, good for you.
In all honesty I was taught to put in a matching transformer, they cost about $3 and it seemed reasonable to do.
Maybe its not needed, I don't know, its just what they taught me to do and I've always done it that way. Sorry if I gave bad advice.
