I've had the DCC sound Thomas and Percy in my possession for over a month now, and I've had enough time to digest them and come up with a verdict.
I was pleased to discover that that they kept the added weights in Thomas much like his analog sound counterpart, and he's the smoothest running engine out of the two. Percy isn't nearly as heavy, but he still has some additional weight to him. I can't tell if it's from the speaker or not though. He's also a little bit more finicky than Thomas with his function responses, which I think can be chalked up to his short wheelbase.
Obviously, these both utilize the exact same soundfile used on the G scale variants. Bachmann confirmed this would be the case early last year. That's not much of an issue except that they didn't adjust the chuffs to match HO, which makes them severely out of sync with the wheels unlike the G scale ones. I plan on eventually going in and adjusting the CVs to fix this.
Overall though, these are fairly solid releases. And I do hope to see other engines in the line get the DCC treatment too.