What do all of you feel is the best technology to play background/mood music while DM'ing without interfering with the flow of the game or drowning out the DM's voice while using discord or in person?

for discord my group uses the groovy bot and it works pretty well.

We use Rythm and Fredboat. Both are pretty nifty, and don't really distract from the experience. 

We sometimes set up Fredboat for ambience, whereas Rythm is used for music.

Always found it to interefere with the game.

Only time I use it is non-combat.

Or if I want to have them fight in a thunderstorm etc, where the players can not talk to each other.

Quote from Raisedfist >>

What do all of you feel is the best technology to play background/mood music while DM'ing without interfering with the flow of the game or drowning out the DM's voice while using discord or in person?

In my experience, the best way online is to not do it. I've found that even quiet music interferes with voice communications.

In my experience, you could create an unviewable music command channel then use octave (I think it's the best music player), and play ambient music.