best sub to match SF olympica 3

Hello members !!
I want to add pair of subs to my current stereo system, witch is pretty simple .
PS audio directstream DAC connected directly to belcanto REF600 monoblocks via XLR and then to SF olympica 3 speakers.
I’m wondering witch connection would blend better. High level input from belcantos or low level RCA from PS audio DAC ?
Not looking for anything big and boomy, rather something smaller in size and musical. 10 inch driver subs.

any advice ?

BTW. small/medium size room.