The main difference between these speakers is how deep they play and the amount of bass they can convey.
1961 Tower has a vent in the rear and a significantly larger cabinet, so it will naturally be better suited for setups that don’t have subwoofer(s). The 1961 Monitor is a sealed enclosure that naturally rolls off around 70Hz, which makes subwoofer integration very easy.
Let’s assume you have one or several subwoofers. In this case it will depend where you can place the subwoofers in your room. If you are only able to place the subwoofers behind or to the side of the listening position, then you will likely have a better integration using the Tower speaker as you can set the crossover frequency lower and thus it will be harder to locate the placement of the subwoofer(s).
If you have subwoofer(s) placed on the front wall where the speakers are, you really have no need for the larger Tower unless you are using subwoofers from other brands that are not as dynamic and tight sounding as Arendal Sound subwoofers are. Our subwoofers will meld into the soundstage of the Monitor speakers making them sound like huge speakers. There is really no gain opting with the Tower speakers in this configuration, well unless you simply like the looks of them.