How to route from mixer to PC when using outboard equipment
Since your question is not very clear, I will answer generally and then improve my answer if more information is supplied. First of all, it is important to mention that there are 2 types of audio effects: 


Parallel effects -  used with the original signal, without changing it. For example if you use delay or reverb; your signal gets routed to the effect and then returned back to your mixing console. At this stage - you decide what will be the correct mix between the original signal and the effect. 
Serial effects - affecting the whole signal, for example compression. Auxiliary channels in consoles are usually used to work with parallel effects. You send the original channel through aux to your effects processor and then route the processed signal(actual effect)  back to your return input. 


I say that to imply that usually you will not use your auxiliary sends and returns to use them with external pre-amp. The signal has to be pre-amped before going into the mixer channel, long before it reaches aux send point.

Regarding your question about direct outs and aux returns - yes, both of them will output the same signal as long as the aux volume is at maximum since both of them are post-fader.

If you want to use your external pre-amp with your mixer, you can use the line-in input which, in most mixers, is skipping the built-in pre.

EDIT1:
In some mixers the aux send\return are utilized by only one insert point, however internally tip is used as send and ring as return. This is from your mixer spec: