HI @glai
The SE uses all discrete amplifers, the best [sounding] amplifiers ATC makes. More esolution, finer detials are more clear, etc.
Yes ATC has made external amp actives for a long time. IN the pro side they make the SCM200 and 300- both use an external 3 channel power amp for each speaker. There are tower versions of these for home using a different tweeter (ATC vs the AUdax super high power one for pro) but it still uses the P4 external amp/crossover package liek the pro version. Tjhese sound great but use fans to keep cool so not the best for living rooms, bu better suited to a machine room where they can be remoted. RIght now they make a 150LE that uses a 3 channel, passive cooled P6, with intergrated crossover, so this is an "external active" solution that functions the same as our internal active set ups.