here are the specs of the older SA series ....
SA-5800 Amplifier - This was the entry level integrated amplifier, available in 1979 and 1980. It featured 25 watts per channel, low distortion, and the cool blue power meters. The controls are pretty basic, with 3 inputs (Tuner, Phono, Aux), two tape monitors, bass and treble, and a loudness switch. The SA-5800 sold for $200.
SA-6800 Amplifier - The SA-6800 offers 45 watts per channel at 0.03% total harmonic distortion. Basically, this is just an up-rated SA-5800. The only additional control is a tone defeat switch to bypass the bass and treble controls. The SA-6800 was offered from 1979 to 1981, and sold for $300.
SA-7800 Amplifier - The SA-7800 was the first of Pioneer's Non-Switching Amplifiers. Class A-B amplifiers essentially have a mirrored set of transistors to amplify the positive half of the signal separately from the negative half of the signal. This is very efficient, but it causes cross over distortion when the signal transitions from positive to negative or negative to positive. Pioneer came up with a method to eliminate this cross over distortion, resulting in a 65 watt per channel amplifier at an amazingly low 0.009% total harmonic distortion. In addition, the SA-7800 featured a number of additional user controls, such as low and high filters, two sets of speaker outputs, tape dubbing, and a mode selector (for stereo, mono right, mono left, left + right, or left/right reverse). All this came at a cost $450.
SA-8800 Amplifier - The SA-8800 is an up-rated SA-7800 that features 80 watts per channel and the same non-switching technology. The only additional user feature is knobs to set the phono cartridge impedance and capacitance load to match some of the more esoteric phono cartridges that were available at the time. The SA-8800 sold for $550.
SA-9800 Amplifier - This is Pioneer's top of the line x800 series amplifier. It puts out 100 watts per channel at the same ultra-low distortion level due to the non-switching amplifier. Additional user controls include a switch to dim the blue power meters, and turnover controls for the bass and treble. Turnover controls set the frequency where the tone controls take effect. This allows you to do more complex equalization without having to add an external equalizer. This was the ultimate in integrated amplifiers during the silver era, with the ultimate price tag of $800.
hope this helps .... but do more research and make sure that the amp works properly before bidding on ebay .... also look at the other makes such as Yamaha, Technics, Sansui .... some really good bargains around if you are patient