Dual 12v SMPS

[schiller]

I would like to try an smps with a conventional ss amp (+12v -12v).
Here:
wiring smps in series

is stated that a pc supply can be modified for this task, but after i looked at the schematic of an ATX unit,

http://www.smpspowersupply.com/ATX_p..._schematic.pdf

i saw that the output voltages (12 and 5) are fed to the pwm chip (feedback).

So replacing only the diodes for the -12v with suitable ones and enhance the filtering is not going to work properly?

Any help will be much appreciated, thanks in advance

Konstantinos