I used to be able to get sound on a bluetooth speaker while racing using the Scaley app on my iPhone 6s. I know for sure because I posted this thread at SFI when I discovered that turning off the ringer would make the app go silent, even though music would still play: https://www.slotforum.com/forums/index.php?showtopic=182842
Now, I cannot get sound from the Scaley app out of my bluetooth speaker, regardless of the status of the ringer.
I can get sound from MA2 (Magic Arc App, described in this thread: https://www.slotforum.com/forums/index.php?showtopic=176930 and available at the iOS app store, Google Play, and the Windows 10 store). Interestingly, I can now get sound from MA2 even if the ringer is turned off, so Magic must have fixed that.
Sound is nice, it might be worth giving Magic's app a try. It has a landscape display mode, track call activated by a button on the controller, 16 million user selectable colors for folks with color perception problems, fixed or dynamic leaderboard, and supports multiple pace cars. You can speak directly to Magic for bug reports and feature requests.