I'm not sure what you are alluding to here.....

From a fluid mechanics/heat transfer stand point, there is no benefit to running a push pull type of config.

It would be more beneficial to use two fans in a pull config over using those same two fans in a push/pull config. You will get better heat transfer and will flow more air using the two fans together rather then pushing and pulling.

This is of course assuming that you have a relatively normaly shaped amp rack (a rectangle), it's fairly well sealed, and lastly, the inlet to the amprack is free of obstructions.

You will gain no "crossflow advantage" if you throw one fan at one end pushing and another fan at the other end pulling.