Using MSFS 2020 and all works great (voice command) until I am ready to pushback, then it seems as if the default pushback takes over.  Pushback starts without my voice command.  Any way to disable the default pushback?-if that indeed is the problem.

Also, before Push Back express all of my sounds were coming through my speakers.  Now using a headset and only sounds are coming through it.  I'd like sounds to go back to my speaker except the communication between me and ground.  Is that possible?

I suspect that the way the pushback goes is limited by the way the main FS program works and being a bit stuck with what that allows. I'm guessing this is the case because the procedure departs from reality a bit, in that you release the brakes to set things off, whereas in actual real-world operations, the brakes (and indeed the nose chocks) stay on when the tug connects, then once you have your pushback clearance, the ground crew check everything is clear take the nose chocks off, then they ask you to release the brakes, then they confirm it with you, and then they tell you the push is commencing and that's when you put the anti-collision beacons on (sometimes crews stick the beacons on to let you know they have clearance, or if they are in a hurry, but this is just one of those things you get used to). I'd like it to be more realistic in this regard, but I think we have to accept that it is about as good as it can be given the constraints it is under from the main program.

Pushback crews also invariably don't give you clearance to start the engines until you are completely off the stand, over the road system, and actually on the taxiway, since there is invariably less danger from FOD ingestion if you don't crank until the aeroplane is on the taxiway. Crews of modern airliners don't especially like this, since NEO engines take a while to crank and it means they're not always quickly ready to taxi by the time they are at the tug release point, but unfortunately 'them's the rules' and the ground crew could potentially get in trouble for allowing engines to commence cranking on the stand, as you need special ATC permission to do that because of the risk of thrust from the engines acting on the roadway behind the aeroplane, which would be risky if a car drove behind the aeroplane. The only exception to that, is with turboprops, which can crank an engine without the propeller engaged and may have to start up whilst still connected to the ground power if they don't have an APU (ATR-72 for example).

Maybe the developer could have a word with Asobo in future to see if there is a way this could be altered, but I suspect Asobo have bigger fish to fry at the moment. I'm sure the dev will be along to comment about this with more knowledge about the the matter, but I bet I'm not far off the truth with the above.

Thank you for great explanation.  I actually found the culprit in General Q&A:

Q: In FS2020, can I have the built in co-pilot enabled?

A. We recommend turning it off.  If you're at a gate, the built in co-pilot will automatically trigger the stock pushback system, not our system.

My co-pilot was turned on in communications.

Glad you got it sorted 😉

For your sound, on the setting panel in PBE you can select your audio device for the PBE sounds.