the SVS rca out i think is not filtered and, even if yes, would imply a double conversion ad\da which could bring some quality degradation
I emailed the bluesound and they replied:
when the sub out is on, the crossover cut is done by the internal DSP before the D\A conversion, this is a good news as it means that there are no risks of quality degradation
then is possible to move the cut from 40 to 200 hz, large flexibility to make some test
the cut slope is 12db, which is acceptable i guess
So, Im not experimenting this setup (sub out to Subs and main rca out to the audio research) with frequency cuts of 40\50\60 with good results... of course i will test also more cuts in time
In this way, no additional devices in the between pre and amp... and no double conversion ad\da ....
Then, of course i know that if i really want to make a giant step then i should buy floorstand speakers... maybe i will...