Sealed speakers with a second order sub-woofer high pass will mate well. Anechoically you'd want the roll-off points to match, although in your room you may want asymetric roll-offs.
If you have enough adjustability in the sub-woofer low pass filter, you could just split the DAC output with one connection to the power amp and one to the sub-woofer input. If not you could use a passive line level solution, sold commercially as "fmods" for car-audio.
Ported speakers unload below the tuning frequency and really benefit from electronic removal of lower frequencies.
You could probably use the same splitter with a passive line level high-pass on the power amp input. Many sub-woofer amplifier ubnits include high-pass filters, but they tend to not be very adjustable.
An external sub-woofer cross-over would be ideal.
