help integrating a musical sub for minimonitors

just picked up a pair of B&W CM1's

never had a stand mounted speaker before and woould like
a fast musical sealed sub to give me a little extra bass
also i would like to reduce the stress on the cm1's so that they
dont have to produce the lowest frequencies so they can concentrate
on the midrange up

my problem is i did not like the B&W sub offerings i heard
i have to drive quite far to hear a rel sub mated with the cm1's
and i won't have time to do that for a few weeks

i am not really a newbie but i have never had a sub hooked up
to my system nor have i ever had an av receiver

my system consists of an amp and a preamp

from what i read i think i need a sub with high pass and low
pass connections to provide the lowest frequencies and to relieve
my minimonitors from low bass and midbass duty?? am i right ??

how would i hook this type of sub up tp my preamp as i only
have one set of unbalanced connections
although i do have a tape monitor connection if that helps
but no subwoofer out or bass managemant capabilities or even
tone controls on my preamp
i only have one set of left and right outputs on my amp also

can this be done effectively?????

thanks for any help or suggestions