The sounds for hitting a block are ok, but the match sounds are indeed very bad... at least the standard sound effect "chimes".
"circuits" is a lot better, except that then the block hitting sound effect is bad.
Therefore I mixed up both sound file directories, so I use the "chimes"-sound-effect for hitting, "circuits" for matches, and custom made sounds for "power fail" and "overfill warning". Those custom sounds are actually just a modification of the overfill sound - I wanted to have something that always stands out and is immediately noticable it, since the standard sounds are not suitable for this.
And yes: Some volume adaption of the sound effects to the song volume would be great - harmony adaption would probably be too difficult and simply unnessary, I prefer anharmonic sounds anyway.