certainly the master volume is a real pain in the neck but can be easily solved with a volume poti which is linked between the Pre amp out and Power Amp IN, basically allowing a more sensitive volume adjustment, see http://stinkfoot.se/archives/2159 I used a 100 k ohm log/Audio pot and it works great, makes the amp soo much more responsive. see also attached diagram
Hope it helps!
Juergen
www.juka-sound-craft.eu