Mcintosh mx120 vs 121

What does the mx-121 have that the 120 does not. I found the mx-120 for less then 800 at a local store and trying to figure out if its worth it or save for the 121??
The 121 pass thru 3D on the video side, The 121 is offered as a lesser priced MX151 where as the the 120 really was closer to the MX136. So I think over all the 121 would be a better performer on surround calibration.