What frequency do you have the sub set for?
Since my sub and room are entirely different from yours I don't think it will matter, but mine has ended up at around 40hz (corrected when I checked) so there is definitely some crossover frequency.
For a system without a 2 output preamp, is the only way to hook up a sub by plugging the preamp outputs into the sub via long RCA interconnects, then connect speaker wires from the sub outs to the main speakers? Does the signal coming out from the sub to the mains get processed by the sub's amp as well? If so, this does not sound like a good approach. Is there any other way to do a sub in a 2 channel system without molesting the main speaker's signal with the sub amp? Hope someone can help, thanks.
Bob - No; you can get a Y-adapter for your preamp which will yield an extra set of outputs if you want to try running your setup differently. As you have it set up the signal goes through the crossover circuit in the sub and is fed back to the amp with the frequency limited at whatever the Xover is set at. Yes, this does put the signal through a path that has the potential to degrade it...or "molest" it as you put it.