PP Parallel either makes the foolish design choice of removing the individual bias adjustment or it does the job of driving the individual bias circuits poorly.Of course this leaves the final option of doing a good job of driving a low impedance load like individual bias circuits but this is an obvious and expensive choice. Picture cathode followers or 6BX7 or 12B4 or 5687 driver stages. None visible on the Manley....
cheers,
Douglas
that's why I DIY; cheaper and *FAR* better engineering talent is available....and of course only the end user has input on the finances.