Hi, for those interested in active speakers solutions, here is a setup based on the PreAmp S50Pro+.
I use an active filter from MINIDSP to drive 2 class D power amps. The ACTIVE Sub being connected directly to the SUB output of the S50 Pro.
Main “weakness” in quality is the signal path: S50 Digital => Analogic OUT => MiniDSP Digital => digital active filtering => Analogic => Amp. A long suite of conversions through RCA connexions. But, it is of better quality than with the optical digital connection from S50Pro to the MiniDSP filter…
Certainly because the S50 Pro DAC is 24 bits, as the MiniDSP ADC input, but the S50Pro optical output is not HD as far as I understand. Experts input is welcome 
The circuit:
