I don't think Burke was involved. I used to be a little flip-floppy on it in the past year or so, but after seeing his Dr. Phil interviews (so far) I'm even less convinced he was involved. The revelations that a) John used the flashlight that night to put Burke to bed and b) Burke admits to going downstairs to play with a new toy are huge to me. Burke only says that he went down to play with his new toy, not that he actually ended up playing. Also, it's super weird to me that John would put his kid to bed using a flashlight rather than turning a light on. I think Burke was telling the truth about going back downstairs to play, but he omitted the truthful timeline of events. I think he went downstairs hoping to sneak in some playtime but came upon his parents instead. John had the flashlight in his hand (either because he'd recently just used it to hit Jonbenet or because he took it from Patsy after she'd used it on Jonbenet) and took Burke back up to bed with it, not turning on any lights on the way in hopes of keeping Burke from seeing any more of a scene he shouldn't be seeing or possibly blood on John's hands/clothes.
Burke, in my opinion, is innocent of Jonbenet's death, but he sure as hell knows his parents are responsible for it and he's had to live with that secret for decades now.
Also, in regards to possibly hearing Burke on the end of the 911 call - it's hard to tell what, if anything, is being said there when we've been fed what to listen out for on the recording in advance. But it DOES sound like Burke saying "what did you find?" If that's the case, to me, it helps prove he wasn't involved in what happened to Jonbenet. If he'd been the culprit and talking about the ransom note, he probably would've said something along the lines of, "what is that?" because he would already know what happened to his sister and wouldn't be expecting there to be a note "left". But the fact that he may be saying, "what did you find?" seems to me like he's asking a general question, like, 'what's going on'/'what happened'/'what did you find that's causing you to act like this'.