Allow me to jump in with my own personal comments.... Do not let Bose store personnel tell you that ST120 or even ST130 are 4K compatible. They are not, maybe in the future but not today! The only way you can enjoy true 4K with either of those units is for you to run a HDMI 2.0 cable direct from your cable/satellite to your TV ARC input or my case that I own a Samsung 8500 series direct to their cumbersome "mini connect unit". Then you run an optical cable from your TV output to the ST120 console optical input; start your TV & then you start your ST120 by pressing the TV button. You now can enjoy 4K at its fullest. FYI, if you have directv, you are only getting 3 channels; 104, 105 & 106.
Another thing to consider, if you have other devices, viz. playstation, blue ray, etc. you will need two HDMI cables; one as described above & another one for your ST120. Those devices will not work (seeing a picture) if you are still connect direct to your TV (your Bose on TV mode). You run all those cable direct to the Bose module & when you are ready to watch your blue ray, you switch the cables in your TV & press BD-DVD in your Bose remote; what I have done is to mark the HDMI cable that I use to watch my blue ray & the other one I use to watch 4K.
I understand this sounds super complicated & no-sense whatsoever when you are planning to spent precious $$$ in this new system but Jerezanito that is the way I currently enjoy my ST130. Good Luck,