My setup works like this:
1. All lighting (overhead and LED) is Phillips HUE. I have ST motion sensors everywhere.
2. Hub is SmartThings. I don't use Alexa or Google voice for anything.
3. Harmony Elite remote/hub is primary control...although any tablet/smartphone works too.
This is the workflow that I've ended up with as it's reliable.
I have both an LCD panel and 125" drop down screen/projector...so there are a about 10 different "Activities" to choose from on the remote. For this example, "Projector - Kodi Box" is selected. Here's what happens:
1. Harmony is integrated with SmartThings.but all it does in ST is turn on a virtual switch. When turned "on" this virtual switch then kicks off a number of things in ST which are all lighting related.
a. All basement lights are turned off, but theatre front/rear LEDs are transitioned to blue color and dimmed slowly over about 30s using CORE in SmartThings. The LED's behind screen are 100% turned off, but the rears are left on (blue) at 5% brightness.
b. The ST hub's mode is switched to "Theater" so basement motion sensors just trigger one of three stairwell light (fully dimmed) just for safety if someone needs a bathroom break, snack run etc.
c. Smart switches for the fireplace, and powered subwoofers are turned on.
d. AC infinity fan unit for amps is powered up (smartswitch) in auto mode.
2. Harmony then takes care of everything else via IR hub and remote blasters:
a. Projector is powered up.
b. Acoustically transparent Screen is lowered over LCD panel to cover front wall.
c. Denon amps (x2) are powered up and set to appropriate input (in this case the Shield box).
b. Shield is powered up.
If you press power off on the Elite remote..it reverses everything and brings lights back up dimmed so your retinas are not blasted :-)
This works very well and based on a lot of research and experimentation, is about as "lean" as it gets. This also takes advantages of the strengths of both Harmony and SmartThings.
This setup works great. I use the virtual switch in SmartThings to trigger automations as it results in "instant" responsiveness in that you're not waiting for device polling in ST. If for any reason things don't work correctly, Harmony has a "help" option for every activity that walks you through a guided power up/down sequence. I do have the smart plugs and lights programmed in the the Elite remote buttons (there are four available) so that "manual" control of all lights/smart plugs is possible.
The motorized acoustically transparent 125" screen is retracted here, but basically covers the entire front wall.
There are six HUE led spots and 10ft of HUE light strips at front and rear. The entire basement area is also lit by smart LEDs so they are all managed during theatre mode so there are no sudden blasts of light if a cat walks by :-)