I think that you are correct about the volume control issue with Grouped players and the TV remote, but I'll check that to be sure. Unfortunately, I'm not near a PLAYBAR at the moment.
With respect to synchronized play, there is no significant "drift", this is the cornerstone of the Sonos networking. The synchronization is within about 2ms over the long term. The issue that you might encounter is that there is always about a 70ms delay between a Line-In and output from a player. This is done to to provide provide some time to prepare the signal for transport and a little slack for varying network conditions. PLAYBAR cuts this to about 35ms for the surrounds and SUB. If you attempt to Group PLAYBAR with other players, you'll have a 35ms issue -- unless you adjust PLAYBAR's audio delay. The original purpose of this adjustable delay was to allow some ability to compensate for various delays associated with video processing, but you can use this delay to slow down PLAYBAR to match the Group.
I wish that Sonos did not associate the word "BOOST" with wired networking. This creates a lot of confusion because BOOST is not required. In most respects BOOST is just another SonosNet mesh client, but with the audio inputs and outputs stripped out in in order to reduce costs. BTW, BOOST uses newer, more potent wireless technology than BRIDGE, however, both offer identical functionality.
