Technics has always had just about the best "on board" sound system of all the portables, and I think you will find that very little amplification is needed for the senior set, if any. Mosy larger activity rooms have a mic and you can position it right over one of the speakers on your keyboard. For a nice small setup, you can get away with any 30-100watt amp that has a full range (tweeter prefered) speaker. A bass amp is OK, but will not produce the high end as well as a keyboard amp.

I do most of these types of jobs with NO external amps. Remember - these are old folks.("seasoned citizens") and they don't like it loud.