The 2300a is a very nice amp. But for not much more than than 1500 dollars you can by a used 2500a which is a more modern design. Just my thoughts
The Conrad Johnson MF-2300a is a great amplifier which will drive your 803's with ease. The 2300a's hold their value very well, and your friend's asking price of $1,100 is very reasonable for the amplifier -- especially since you know the history of the unit that you will be purchasing. I highly recommend the CJ MF-2300a. It has a warmth to it that is hard to find in many solid state amplifiers yet it has the ability to preserve subtle details (mated with the right preamp of course) that are both natural sounding and non-fatiguing. If you don't love it, then you can always sell it and recoup your entire purchase price.
An amplifier usually designed as Class AB; meaning during lower wattage usage (usually 10 watts on demand, up to its limits.
A Class A amp is always running full bore, regardless of what is asked of it, the extra wattage will turn to heat. There is no A to B switching, thus less distortion.
So, Class A or AB has less to do with how much power it can produce, rather it discribes how the amp is designed. Class A is less efficient, hot, but can sound very nice and warm. But,there are good sounding amps using either designs.100 watts of Class A is no more power than 100 watts of AB.
As for the speaker asking for "up to" ( I assume max) of 250W...it is probably telling you not to drive 250 watts into it, which is very very loud. Unless, you are really into head banging music, I would not worry. The amp and the speaker should be a great combo. Enjoy.
Let edit my post above...the first paragraph got cut off. I was trying to say an AB amp runs class A, usually up to 5 to 10 watts. During Class A, it is running to its Class A limit of say 5 watts. If the power is not needed, then the watt is disappated in heat via the heat sinks. If more power is needed, then the amp switches to class B, where it will provide wattage on demand.
I agree with Rich3549. Class A amplifiers are biased up to the point were the output devices are running full tilt all the time. Class A designs use more current and require large heatsinks to dissapate the heat. Not a very efficient design but do generally sound sonically better than class A/B. Class A/B amplifiers are the dead opposite & the bias is set to a predetermined setting where as the output devices runs cooler until called upon for higher volume levels. Class A amps have a tendancy to wear themselves out faster than class A/B amps(eventually requiring replacement of output transisters & caps). Note some class A/B amps are biased up a bit to give you the first 25 watts in class A. The MF 2300A is a superb class A/B amp and at 1100 US is a very reasonable asking price.