If you mean a dual station monitor. The answer is no, they cannot.
The only Raymarine systems that can do a dual station is the C Wide series, E series and the new to be released E Wide Touchscreen series. All of these units would be approx 2.5K, 3K and 5K. (each)
The only way to add a second monitor is to actually buy another DS400x, DS500x, or DS600x and install it there using the xducer cable that already exists. The xducer is interchangeable between all three of those units.
But the easiest way is to do what I suggested and actually add a wire harness for your current unit (DS400X) to the OTHER location and use the xducer at eith location an splice in a connector.
But don't forget, only one station works at a time--as only one unit can operate the xducer at a time.
My suggestion is to just add another depth/fish finder where you want it and keep the xducers on the two different freq's. One 200khz and the other on 50khz. Again, that would facilitate the need to install a second transducer.
pm me for more info if this was a bit wordy.