Ok, the bass towers have a XLR input as well as a XLR output. So basically from the pre-amp you feed into the XLR input. In case you wish to work with multiple subs, you can take the XLR output to feed the next Sub-amp. So you don't go from let's say the left base tower to the right base tower using this output. It could be done, but then you would be feeding the "left signal" into the right base tower. If it were very low frequencies only, you would likely not be able to distinguish the mix-up, however as the cross-over frequency is rather high, you will hear this. But possibly you meant something else ? Bottom line is that you should have four outputs on your pre-amp, so you can feed the four power amps directly from the pre=amp. There is no XLR output on the mid/high towers, so you can't go from there to the bass towers. I'm using 1 pair of short (1 meter) interconnects to go from the L1 to the M1.1 monos, and 1 longer pair (3,5 meter) to feed the power amps in the base towers.