6 dB steps are too coarse. 2.5 dB or 3 dB is about Ok, but then the range is too small with 15 steps. A 24-step switch would be better. If you insist on the existing Plessey switch, perhaps a 30 dB fixed attenuator for the lower range (with a toggle switch for insert/bypass) and 2 dB steps could provide finer control (or 45 dB fixed + 3 dB steps). My listening habit uses two ranges: normal/high volume at 0...-20 dB and background/low volume at -30...-50 dB, and I prefer fine control in both ranges.
