While you technically don't have to follow the limitations strictly, for music you should stick with the limits because they're really not hard and it would be wrong to outright violate them. Playing sounds over the top w/o muting the channels is completely forgivable.
If you use SunVox, that means using a polyphony of 1 for everything and not using reverb.
Here's the channel allocations, by the way:
- 2x 12.5%/25%/50% pulse channels
- 1x 32-sample 4bit wave channel - VERY LIMITED VOLUME CONTROL HERE
- 1x noise channel (15-bit/7-bit LFSRs selectable)
For GBJam3 I was going to target the real HW and stream audio on the wave channel, but I shot myself in the foot when trying to get the actual gameplay in, so I didn't end up entering.
Also, I'd probably end up using SchismTracker for stuff w/ a suitable packgen.