I spent time with all three back in the 1980s and still have an SP10 II. The SP8 is similar, only less transparent, less extended, and less dynamic. But a good friend sold his 10 for an 8 because he found the 10 too revealing. His SP8 II/D70 II sounded very good. Both SP8 and SP10 are all tube designs. The 10 comes with a separate tube power supply in the same size enclosure. The SP9 is a hybrid design and more hi-fi sounding but still pretty good. The 10 was famous for that opening line in a Stereophile review: 'Sell the Mercedes ...'