Another Bluetooth Audio Question

I know there is a lot of options, but all I'm looking for is the ability to stream music from my phone to the car and be able to forward through the tracks with the steering wheel. I don't care about handfree calling, just music. Is there an affordable option out there?
I currently have a unit that I bought from Ebay that works but the problem is whenever I'm streaming the passenger door speakers sound does not come in fully. I'm attributing this to the unit as I just installed new speakers and they still aren't full. Or, am I dealing with am amp issue?

Sounds like it may be more of a speaker install issue. Check the speaker connections and polarity in the passenger door.

Did you have sound from all the speakers before installing the new ones? Before installing the eBay unit? You've changed two things so need to reexamine your work. An amp problem can affect speaker output. New speakers can be faulty straight out of the box.