How is the soundbar hooked up? Do you have:
X1 ==<HDMI>==Soundbar==<HDMI>==TV ?
If so, there's probably a setting on the TV that involves CEC/HDMI link that conflicts with the XR11. You could try disabling that, or, since you don't have HDMI-ARC on the TV, I suggest using the soundbar's Optical input and connect it to your TV's Optical out port with your soundbar's included optical cable.
With “HDMI IN” selected, my Xfinity XR11 using code 31937 turned on my Vizio SB3661-E6 properly. HDMI input was from the Xfinity/Comcast wireless cable box. Vizio output was HDMI to my Samsung TV. I had no Vizio apps on my iPhone.