Bryston 14B ST vs 14B SST?

I'm wondering if anyone can help me with the relevant differences between the Bryston 14B ST and 14B SST? I'm looking at replacing my 4B ST and have an opportunitty to purchase a 14B ST from a friend and am wondering if I should hold off and find a SST (if there is a material difference).

Thanks for the help,

Clayeton