I have just bought a Behringer 120FX mixer and Bose L1 Compact PA and will be playing in public for the first time in my life. I started off plugging the three inputs, from midi sound module, computer (for RTs) and keyboard into the mixer stereo channels and I noticed that the sound from the Bose was very heavy on the bass. I then tried plugging in to the mixer mono channels because these channels have EQ controls. This allowed me to adjust the bass going to the Bose but the piano sound from my Yamaha CP33 keyboard had deteriorated whatever I do at the mixer. The piano sounds "tinny" and looses its Yamaha clarity while the midi and RTs sound OK. I get the same difference in piano sound when listening on headphones at the mixer so this means the difference occurs at the mixer, not the Bose.

I am using left and right 1/4" mono connectors between the piano, mixer and Bose with 2/1 1/4" adapters for mono connections at the mixer and Bose.

Is there a correct way to route these three inputs through the mixer?
Does it make sense that the keyboard is better through the stereo input and the others can go via the mono or stereo input.
Is it normal for the Bose L1 Compact to sound so bass heavy? My Yamaha piano sounds wrong unless I apply some EQ.

Thanks
Tony