Audio trouble

Started learning about audio circuits.   Dang.   The basic digital stuff I've done was all Tab A into Slot B plug-and play, but analog is quite different.   I've familiar with the most basic of concepts, but the interaction between components is wrapped in a hazy mist of math and magic.

After learning about audio mixers, it's clear that I want to make an active mixer, one that sums the inputs with an inverting opamp.  If I'm reading right, this will ensure that adding and removing inputs will not change the overall level of my output.

I have a dream of powering this whole device from the 5V 500mA USB supply, so I'm at a disadvantage when it comes to analog part selection.    Picked up a couple of cheapo opamps that claim to work at low voltage. Wired an audio signal to my breadboard, plugged the things in as per the datasheets, and BWAAAAARRRRRRAAAHHHHHARRRRRRRRGHHHHAAAAAADZZZZZZ horrible noises.  After a few hours (days) of reading and reconfiguring I have actual audio passing though the thing, but it sounds like stir-fried ass. I am doing something wrong.