Pretty much anything from Klipsch would work.
the key is high efficiency 94db+ and stable 8ohm load. The older SS Sansui's did not like to push lower than 8ohm loads so no 4ohm speaker here. Also if the receiver has not be serviced yet get it serviced soon they had some caps that will need replacing now. That said they are a nice little vintage SS amp that sounded a lot like tube amps from the day.
The Dayton recommended above may not be an ideal fit for that amp its 6ohm and not very efficient. ok on a desk top probably.