You need to take account of power and impedance of the speaker from Freeplay kit.
I think it is a 1W 8ohm speaker (not sure for the power).
If the speaker doesn't match power, you will have a volume difference between left and right.
If impedance doesn't match, the audio driver can have overheat (unlikely in your situation).
Quick note: speaker only output one channel, I don't remember if it is left or right (it is difficult to combine stereo to proper mono output without adding a negative voltage source and a opamp).
I think it is a 1W 8ohm speaker (not sure for the power).
If the speaker doesn't match power, you will have a volume difference between left and right.
If impedance doesn't match, the audio driver can have overheat (unlikely in your situation).
Quick note: speaker only output one channel, I don't remember if it is left or right (it is difficult to combine stereo to proper mono output without adding a negative voltage source and a opamp).