I'm not familiar at all with any Spider amp before the Spider III series, but I suspect that your amp suffers from the same problem as the Spider III, IV, POD 2.0, POD XT Live and X3 Live and other DSP based devices - VIBRATION.   Vibration from loudspeakers can make potentiometers which have become slightly loose with age and wear & tear move very slightly.  With an analogue amp this wouldn't be as noticeable as with a modelling amp where everything is controlled overall by the DSP.  Presets include all settings except Master Volume which on the Spider series amps is the only analogue control.  All the others control what the DSP does.  If you park ALL the controls except Master Volume at zero and change to a new preset you will get the sound you expect at the volume you expect even though the positions of the control knobs suggest differently.  If on the other hand you leave your control knobs at what appear to be normal positions and then proceed to play loudly and say the Channel Volume control is a bit loose and set physically to 75% whereas the setting in the preset for that control is set to 50%, all that needs to happen is for the control to be vibrated to 74% or 76% and this new position information is immediately transmitted to the DSP which simply obeys the instruction to jump to the new setting.  Result = massive jump in volume.

Park your knobs at zero and the problem should be minimised.

Nick

i have discovered with my spider 2 that you can use the headphone socket as line out and plug it into the input of another amp, i have plugged it into a yamaha GA-10 and its great for my bedroom etc,using reverb and whatever effects you want playing through the other practice amp,with or without the treble/bass of the little amp, brings with it a new tone,and if you have a problem with volume of spider you dont have to fear death everytime you alter it,cos you can set it then alter GA-10! great! or whatever your practice amp is or amp of choice im liking it with or without volume issues of spider