If you are wanting to compare the 9000 amp with another then you have to specify under what conditions you are doing the measurement. The usual method is to quote the output with a RMS signal between certain frequencies. The 9000 is quoted as 30 watts per chanel RMS 20hz-20khz at a certain minimal distortion level which I don't recall. This can be directly compared to other amps under the same conditions.
The trouble with this method is that it tended to produce lower figures. Not what the marketing men wanted! This led to many other quoted methods which produced higher and more acceptable but not neccessarily more meaningful figures. Peak power, music power, transient power and many others. The 2x80 watts figure is one of these marketing department figures which doesn't really mean very much.
The 9000 amp is certainly not an "80 watt" amplifier in real terms but does it really matter. I have had 9000's since they came out in 1986 and have used them to drive speakers many and various from CX50 to beovox penta. The crux of this all is that if you want to play music at reasonable levels in a normal domestic lounge then the 9000 is more than adequate if not outstanding. For loud rock in a big room with large speakers it probably is not the best and you would probably need a more powerful amp for the best results.