For VPI owners with 3D tonearm bases

"Is my only choice to get another 3D(seems like I'm trapped with a unipivot) or are there other tonearm options which will allow me to easily go back and forth between arms? They would as you know have to have the cable to go into that rear black box".

Probably the easiest thing to do, would be to buy another arm piece only. The unipivot design makes it very easy to swap out. The only downside is that you'll most likely have to redo the setup every time you switch.  

if alternating cartridges is the aim, then all you need is another (or a few) compatible VPI armwands. I did the same upgrade. With that arm base you can use a 3D arm wand or a JMW 10.5 wand (or Classic 3). The latter are cheaper, and if you get one with upgraded tonearm wiring they won’t be too far off sonically. But do make sure you don’t purchase an older (like version 10) arm wand, because they’re too short.

Thanks!