IOS (Swift) Background speech - ios

Question

I'm writing an exercise app that runs a series of timers back to back that are determined by the users exercises and the times they have entered for them e.g. push UPS for 30 seconds, squats 20 seconds...
When the timer reaches zero, the app speaks the next exercise, and starts the next timer.
The app also allows the user to play music from playlists whilst they exercise, so I have set the Audio background mode in capabilities in swift.
When in the foreground, everything works as expected, and the times, and speech fire when they are meant to, however, when the app is backgrounded, only the music continues and everything else stops.
I understand that Apple have strict rules on background processes and multitasking, but I have downloaded a number of apps that seem to work fine in the background and continue to speak the intervals as they become due (Seconds Pro, Onyx Timer etc.)
I have researched this for days, but cannot come up with an answer, background fetching doesn't seem to be reliable enough for a time based app, as you can't guarantee when it will fire, I've also looked into local notifications, but they don't allow speech when they trigger, just a short sound, they also have a limit of 64 notifications, which limits the amount of intervals the user can set
I have set the app to keep the screen awake whilst the timer screen is running, but this means you have to keep the screen on whilst you train, which in turn will add an unnecessary drain on the battery, which seems to go against everything Apple is trying to accomplish with the limited background activity
Push notifications seemed like one solution, but this would mean I have to setup some sort of external server and surely this would be interrupted if the user didn't have an Internet connection.
I have read multiple threads about people running a silent audio stream in the background to keep their app alive in the background (not approved by Apple), but my app already plays audio in the background and has no effect on the rest of the app being suspended?
How would I go about achieving this?
I have thought of a workaround, but I don't know if it's good practice, or if it will get the app kicked if I try to upload it to the app store
My solution was to queue my speech based on the time set in each timer
for timer in 0...timersArray.count{
let sentence = timer.speech
let speechUtterance = AVSpeechUtterance(string: "\(sentence)")
speechUtterance.postUtteranceDelay = timer.time
synth.speakUtterance(speechUtterance)
}
Then the speech would just trigger at the appropriate times, even though the timer wasn't running in the background
When I ran this code, it worked as expected and the speech triggered when the timer would have finished (just as if it was running)
When running this code though, I noticed that not only did it trigger the speech at the correct time, it also kept my app running in the background, which is exactly what I wanted in the first place.
Is this allowed practice, or will it get booted from the store?
As my app plays music in the background and has the audio capability set, is there a way I can use a similar approach, but with the music in the background, rather than the queued utterance approach.
I tried with MPMediaPlayer, AVPlayer, and AVQueuePlayer, but nothing worked, the music played in the background, but the rest of the app stopped
If I set "Does not run in background" to "Yes" in the Plist.info, the app will now run when the screen is locked, it still won't run in the background though?
There are so many apps in the App Store that seem to run happily in the background, I can't believe it's this hard to get it to work?
A number of the ones I have tried, are not listed under notifications, so I know it's not a local notification, they also work in airplane mode, so it can't be remote push notifications