I have one. I find it an excellent piece of equipment. I cannot tell you how it relates to the 1200RX since I don't have these. The other monoblocks I have are 600RX's. I can tell you that the 1200 Digital pack has about a stop more than the 600RX when used with a SSE head. Naturally you will loose power when you start to extend this cable. Naturally the shorter the cable the less power you loose. I don't have the idea that I noticeably loose power with using only the cable that is standard on the SSE head. Certainly not 1 stop since that would make the 1200 pack effectively having the same pop as my 600RX. It is certainly more, about a stop (which it should be).
I skipped the 1200RX monoblock because of its huge size. If I would have to choose between monoblock and pack it would be the monoblock when I need 600WS (600RX) and the pack when I need more.