How to add and power a Bluetooth receiver to battery powered speakers?

I have a iHome speaker that is powered off 4 AAA batteries. I want to add this bluetooth receiver to the speaker.

The bluetooth receiver is powered off USB, but I want to keep the system battery powered.  Can I take apart the bluetooth receiver and solder the power connections to the power connections on the speaker?  

The speaker is powered off 4 AAA batteries, so 6 volts.  (How many amps??)
The bluetooth is powered from USB which is 5 volts, correct?  

Would the 6 volts from the AAA batteries damage the bluetooth receiver?  What about current?

The voltage tolerance of the receiver may be able to handle the 6V. But you can always by a 1N4001 diode and solder that between the receiver and the power source. The diode has a 1V voltage drop so the receiver would only get 5V from the power source.

The current will look after itself. Use Mpilch's diode and you shouldn't have a problem.