Yep, midi/usb.
Pi : I’m yet using Raspberry Pi as samples player and it’s not trustful at the starting up ( my opinion of user ).
Usb : convenient small inexpensive controllers
Midi : convenient with a midihub midi learning functions. I’ve discovered the UC33. BCR2000 is on paper a good idea ( even more with the seq update mod a few years ago ), but I’ve been a bit cooled by a few people testimonies getting some troubles with it using midi learning mode.