If you have replaced all the transistors, then you have to first double check that all the NPN and PNP are installed in the correct order and nothing is reversed. Next inspect all the solder for bridges or an unsoldered transistor leg. Finally, start checking the discrete resistors and diodes. I believe your posted schematic is just an example and not the real circuit. Look for small value resistors in series with the emitters of the BJTs. These are often used for balancing and during failures will either burn open or change value. Small signal bias diodes often also go open or leaky.
Does the circuit have any balance or adjustment pots? If so these variable resistors may need to be reset to adjust for the new transistors.