don't put sandwich plate TEC,
use them single, dual stage tec is not good on direct die cooling, only for small things like led's and lasers.
Use single TEC more power, 136w is not enough for cpu.
you need something that can cool down the cpu, and a cpu gives overclocked like say 250w,
so you need to cool down that.
Use a minimum of 226w TEC or 260w 50x 50 or 40x40mm.
And cool that down with good watercooling.
Look here in dutch from me :
Chiller's Custom TEC on air
chiller's custom TEC
and offcourse Hybrid TEC cooling, where tec is cooling down the liquid as i use now in my rig Level 10