X15 remote

Thanks for your response, to better understand your problem can you tell us if you had an XR15 remote before? 

I'm referring to the X15 remote that I received with my replacement STB. The old X1 remote I still have hanging around has two power buttons and at least serves my immediate need. The problem is the X15 only has one, and it appears to be capable of powering on/off just one device.

@XfinityAaron​ Cable box (STB)is on all the time, not relevant. I want the one power button on the X15 remote to turn on/off the TV and the receiver with one press. It currently operates whatever device was last coded into the remote: TV or receiver. Pretty simple issue. Can this remote send two power on/off signals to two devices? Does it power on/off two devices for you?

That is a great question! With the XR-15 remote, you do have the ability to turn on and off, both the TV and the box of course, ensuring that the TV is compatible as well! However, based upon previous bits of the conversation here, it appears to have worked in the past for you.
I know it had been mentioned that you've completed the master reset on the remote, which can oftentimes help with any pairing issues. However, have we had you attempt to turn off the pairing, and then attempt to re-pair it again? 
https://www.xfinity.com/support/articles/x1-remote-unpair 
I've included the steps in a link above, if you've not tried that already! Please let us know the results! 

Sorry, but this is quite a circular discussion. YES: I did a factory reset the remote; YES: I tried re-pairing. YES: I tried manually coding each device rather than use the on-screen prompts. NO: please don't refer to "the box" (by which I think you mean the set top box, or STB, which is irrelevant because it never powers on/off; it's always on).

I did refer to an older X1 remote I have hanging around, but it has TWO power buttons, not just one, so it serves for now. I'm sorry I mentioned that as it appears to confuse the discussion.

It is the X15 remote (the newest one with only one power button) that does not power more than one device on/off. YES: the X15 will power on/off the TV or (and the keyword here is "OR") the receiver, but only one of them (whichever was coded or paired last; once a subsequent device is paired or coded, the first one no longer powers on/off).

Please be sure you understand my problem before your next response. The question cannot be any more simple: can the X15 remote power on/off more than one device (TV and receiver; leave the STB out of this discussion!) with a single button push? If so, how can I configure it to do so? If you don't have the answer, try escalating to the engineers who are responsible for the remote. 

If you are confused as to which remote, just search for "X15 comast xfinity remote"; you can retrieve the manual and see exactly the remote I am referring to. The X1 and the X15 are completely different, and Comcast no longer provides the X1. OK?

My apologies for any confusion there!

Personally, I know that when I power my Samsung TV on with my XR-15, the JBL receiver comes on at the same time, and initially when set up, I too, had followed the prompts to pair both.

May I ask, to confirm, you'd mentioned an old X1 remote: Is the first remote on this link what you are referencing?
https://www.xfinity.com/support/articles/get-to-know-voice-remote
Also known as the XR-11 that has the TV power, as well as the ALL POWER buttons?

The XR-15 remote was designed to consolidate the ALL POWER button and TV power button in one, so ultimately should be managing both devices if paired successfully.

OK, so if the power button controls power on/off for your Samsung TV and JBL receiver, I guess the XR-15 sends two signals (unless Samsung and JBL are using the same RF signal from the remote... that's a possibility, but not likely).

I have a TCL/Roku TV, and a pretty old Samsung receiver/sound system. When I first installed my new STB, I followed the on-screen prompts to pair remote to TV and to the Samsung. When I first paired the TV, the power and volume buttons worked on the TV. When I subsequently paired to the Samsung, both power and volume moved to the Samsung, in effect losing the TV. I prefer that volume works with only one device (it works with the Samsung, which is fine). But once the Samsung is paired, the power button no longer effects the TV. You are indicating that the power button should still power on/off both, once they are paired. 

Again, I've tried the on-screen pairing, and "manual" pairing after factory resetting the remote by pressing "A" and "D" buttons > 3 seconds and entering 981 (which appears to reset, as the status light changes color and the TV and Samsung are no longer controlled by the remote). I used the codes "11756" for the TCL. I used "31868" for the Samsung (third one on the list of five codes). No matter what I do I can't get the power button to power on/off the TV and the Samsung; one or the other, that's it.

I'm hoping you have a different procedure to try, but this is a long conversation about what, I gather from your comments, should work (but doesn't for me). sigh