I was glad to see from the spec sheet that the input impedance of the zoom is 1 mega ohm (as opposed to 1 ohm).
I wouldn’t get too concerned about the figures, if you like the zoom it will work fine with the Rtym (and the input sensitivity is the figure to look at). Just make sure to increase the output volume of the Rtym slowly until you get a feel of how loud the combo can get. One thing to note is that the maximum output level of the zoom is lower than the maximum output level of the Rtym.
With regard to line level the common alternatives are devices which output at significantly lower levels such as microphones and the phono output from record players. When using these devices it may be necessary to have a pre amp if your device does not support mic input levels.