Podcasts have some specific features which are not available on other audio content. This is why you can play it from your mobile device, but not from your speaker.
In the other hand, when you listen music through a Speaker, the music will always stream with the regular quality that you speaker uses. The quality settings on your mobile device will only affect the quality when you play music from that device.
Let us know if that answers your questions. Have a great day!
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