P1 I can confirm for the newer XL and XXL models. If you use a warning sound and the same for a POI or speedcam the device goes silent when the sound is played. Same can happen with the TTS voice of Kate, some newer Navcores only accept Susan but not Kate. On several devices the soundmodelID must match the modelID, meaning that in certain emulations the sound goes almost silent (you can just hear it at full volume when you have the speaker on your ear). So far I was not able to find out what causes this problem or how get the soundmodelID and modelID matching in all emulations.
P3 As mentioned by Tendriver, some are premium voices that needs activation, and you might have to check the .vif files and filenames - some user reported that a few voices have the same numbers and filenames like already installed voices. Might be a good idea to manually select the voices you need.