Sansui CA 2000 preamp

Should be a nice preamp. It was one of the first to incorporate low distortion transistor circuitry, and had a unique volume control circuit that reduced noise to very low levels. They don’t make them like that anymore and from that standpoint, it’s worth having.
It’s quite an old unit now so you’ll probably have to service the switches and maintain them over time, apart from upgrading some capacitors. Some of the transistors are hard to get now if they need replacing (not likely unless you get otherwise unexplained noises), but not impossible to substitute with other similar modern transistors. When you get it serviced, make sure you check over the solder joints of the bigger transistors as they generate heat and can crack the solder joints over time, which can lead to all manner of mayhem. If you give it the TLC it needs it will be a good preamp. IME most Sansuis take about an hour to warm up to start sounding good.
I’m a Sansui fan as well and have a CA-F1 and BA-F1 pre-power combo. I replaced the notoriously troublesome black flag capacitors in both of them. Check to see if they are in the CA 2000 as well. If they are replace them too.

Glad it fits into your system well! Especially regarding the low noise with sensitive speakers. 
A low powered amp would work well with them and a single ended tube amp might work well. At 100dB efficiency all you might need would be a 300B amp with typically around 7 watts. Which speakers are you running? What sort of volume do you play them at?
Class D amps are very efficient and put out lots of power for their size, but you possibly won’t need their high power in this case.