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.
i have a mx132. used as a 2 chanell pre-amp tuner. is there another mx that would do a better job for my needs?
I replaced my MX120 with a MX121. I didn't notice much of a sonic difference between the 2 units, but I do like that I can go HDMI from my cable box into the MX121. With the MX120 I went HDMI for the video connection direct into my TV monitor and COAX from the cable box into the MX120. I do like having a newer unit. I only use it for watching TV in 5.1 and think it works and sounds excellent. I really preferred both units over my old Marantz pre pro.