Here's what I can see (attached pics)
1) Softstart switch
2,3,4,5) Codaca CSCF2012 series (CSCF2012-100MC), this is smaller than SER291X series of coilcraft inductors, but just right for the application
6) Single power supply for housekeeping
7) 4 Input coupling caps for TPA3255 inputs, another 4 input coupling caps on the buffer frontend inputs
44pin probably is TPA3255 since the voltage is 38V, components like OC_ADJ 22K ohm resistor is on pin 7, FREQ_ADJ(600kHz) 10K ohm is on pin 8, etc..
Engineering efforts that were made here are on the PCB layout itself as well as the PFFB section on the input. It uses multilayer PCB which is more expensive.
Cost cutting is done on the housekeeping power supply, he can easily use dual supply for the opamps. But using dual supply can add significant cost on BOM.
Here's a comparison with my Sylph-D400 100W 8ohms / 200W 4ohms / 400W 2 ohms. With passive PFFB from TI notes, it can only get -97dB THD+N on 10W 4ohms.
I believe the next Topping PA amp will have a similar power output.