The master volume control CV is CV58, its values range from 0 to 15. The factory default value for this is 09.Digitrax SFX decoders have a factory default value of 09 set for CV58. This works well for 32 ohm speakers.The decoder will reset to this value whenever you do a decoder reset of CV8=8. Digitrax SFX decoders built for use with 8 ohm speakers should have this value changed to 4 or 5 for best operation value of 4 or 5, since the decoder may not supply enough current at high volume/drive levels.Your results may also depend upon track voltage present. Kato USA says ...