Main box: XG2v2-P model PX022ANM
Secondary box: XiD-P model PXD01ANI
I don't know anything about the XiD-P other than this:
Since it has to use the tuners from the XG2v2, I would prefer a second XG2v2 instead. Any chance you could swap it out at your nearest Xfinity Store? It should be a free swap and I believe they show up on your statement as costing the same.