The maximum volume setting is probably +10dB, but how loud that is depends at least on part on how you calibrate the unit. The standard approach is to set the unit's volume at 0dB and use the internal test tones to adjust the individual channel levels so that they all achieve 75dB on a sound meter held at the listening position. When calibrated in this way, setting the volume to 0dB would exactly match the volume level of a movie theater. Most people calibrate this way and then watch DVD's at a volume less than 0dB. Videodrome is pretty typical - he listens at -15dB to -5dB. If it's just me watching, I tend to listen around -15dB to -10dB, but if my daughter's asleep down the hall I might keep it around -25dB. (I use a 990 instead of a 970, but I calibrate to 75dB and I've ended up using the same basic volume settings with both my 990 and the 950 that I had before that.)

DVD's will generally warrant a higher volume setting than CD's and TV viewing, because DVD's are recorded at a lower level to provide more frequency response (they have more headroom to cope with sudden spikes of volume like those depth charges Videodrome mentioned).