So, you took out the connection that is the red line and added the connections that are the two yellow highlighted lines on the left. I don't understand why you did this, because they do the same thing.
The only real change seems to be that you added the right channel amplifier on the right. I'm wondering why you didn't just short the left and right terminals on the stereo jack and drive both from the left channel amp. Anyways, perhaps the problem lies in that you have attached a second DC source to the junction in the middle and the DC bias is now upset and needs to be adjusted. A check of DC voltages on the various amps should give some clues.