Both the common ground and the decoder positive are NOT on the six pins. Those pins are track-power (2), motor-power (2), front light, rear light. That's it. (The positive power for lights on a six-pin comes by half-rectifying the track power when it is returned via the relevant lighting wire).Unlikely. The common ground connection is on one of the six pins if memory serves, and the other connection is probably somewhere on the decoder board, there may be a solder pad if you are lucky! (I'd suggest researching that before purchase, and I see you have just spotted another 'trap'!)
The more I hear about the 56xx and its decoder socket the more one dispairs.
Alternative small RailCom capable decoders include the smaller models from Zimo and D&H. Both tiny and may fit without needing right-angle pins.
( I disagree on Stay-Alives, they transform the running quality of smaller models in 2mm, 4mm and 7mm scales. These are models with all-wheels picking up reliably, carefully laid track with live frogs, etc.. And, I've had a fair few skeptics saying "not necessary" who come round to ordering retro-fits in their locos having seen what locos do. Its not about running over a sheet of A4 - a pointless party piece. Its about fractions of a second of hesitancy. ).