I recently added a powered sub to my two powered Yorkville Skrs. It is the NX200S. Has 200watts, 1-10" spkr. 54Lbs. very compact. Adds so much to the overall sound. I run my SD1 in stereo, into a Mackie 1202 L/R output to powered Yorkvilles on stands.
The Mackie has two, effecta and monitor, sends for each channel. Both sends include EQ I use send 1 for the Sub and send 2 for the powered monitor (Fender 1270p) The send for the sub sums left and right, very cool, so I get full input into sub. The diffence in sound with the sub is tremendous