Hello there! My name is Ismael J. López R. I am a professional sound engineer with three years of experience in sound-reinforcement systems design and installing for bars and restaurants. I would like to be part of your project and help you with you issue.
There are plenty variables than can be causing the problems. However, I think that I can help you completely remotely without going to your coffee shop. I've been a Spotify user for five years so we can start discarding variables from there, because if the problem is there, you will not have to replace your speakers. If you're replacing them anyway, I would only need you to tell me the reference of your current speakers and the ones you're about to purchase, so I can guide you how to connect your system properly.
Contact me if you're interested! Looking forward to having news from you.