I have just looked at this thread and the photos of the mixer that the originator has and the request for information.
The mixer has XLR connectors for BALANCED MICROPHONE input. If you put any form of line input into these (ie -10db, +4db, etc) you will greatly overload the microphone input (like connecting a 110/240V supply into a 6V torch globe or similar).
You will note that each of the inputs just below the XLR connector has another input socket (1/4" -- 6.5mm) that is marked "Line". THIS is where you should be connecting the XLR line outputs from the pre-amp unit (forgotten the make/model). More on this below!!!!
You will also note that the "line" input on Chnl 1 is marked as unbalanced. This is for things like a mono feed from the line output on (say) a guitar amplifier or possibly the mono output from a synth, etc.
The "line" inputs on Chnl 2 + are marked as balanced/unbalanced --- this is where you should be connecting the XLR outputs from the Pre-amp unit, BUT you will need the following.
As the pre-amp has XLR outputs, the outputs will be balanced (ie +ve & -ve wires), so you will need a balanced XLR lead (pin 2 hot, pin 3 cold, pin 1 earth) to a balanced (ie stereo or TRS) 1/4" jack plug (wired hot to tip, cold to ring, earth to sleeve) and you will need two of these leads (one for each of the pre-amp outputs) and you would plug these into (say) Line input Chnl 2 & 3.
Now (for the first time at least --- until you know that all is OK) before turning on the mixer's power switch I would be connecting everything up and have a good level signal coming from the pre-amp, then I would be raising the level of both the respective channel faders and the master fader to the marked 0Vu point on the fader and turning the channel Gain control to the fully counter-clockwise position (marked -20). Now I would be turning on the mixer's power and then slowly raise the level of the Gain pot on one of the channels until you get light on the signal LED and reading on the master Vu meter (NOT 0Vu but say 4 or 5dB below), I would now lower the channel fader for that channel to the minimum position. Now raise the level of the other Gain control until it gives good signal (again say 4 or 5db below the 0Vu mark), now while leaving the second channel set, raise the level of the first channel and you should see the master VU meter start to rise and hopefully when the first channel fader gets to its 0Vu position, the master Vu should be around the 0Vu mark.
Now depending upon the signal being fed into the mixer you will most probably have to adjust the levels of the Gain control and channel faders to get the exact levels you require for the song you are mixing/recording ---- this is called "mixing".
Although long winded I hope that the above puts the originator in the correct position with his set-up and is not too confusing and it is has been presented this way and in this detail as I am presuming that the originator is just starting out and is not familiar with audio electronics, console operating (especially gain structure) and recording/mixing techniques.
David