Best Tube Preamp with Biamp Capability

Do yourself a huge favor: keep your SP11 and go with an
active crossover instead. Removing the passive crossover
components from the amp/speaker interface is the best way
to improve any speaker's resolution. Unfortunately you'll
still have the mid/tweet components in the signal path but
you would still realize greater improvement in sound than
simply vertically biamping with the passive crossover. You
can get a top flight active crossover for far less than a
top pre. Most active crossovers will allow different slopes
and frequencies (24dB @ 220hz is what you'd need). Since
you've already got the amplifier channels available, this
is the only time I can remember that setting up for active
biamping will be less expensive than setting up for passive.
Give the active a try. You will not be sorry.

Sorry the SP11 must have been from another thread. I don't
think you mentioned what type of pre you are currently using
but judging from your other components I'm sure it ain't
chopped liver. Keep the pre, get yourself an active x-over
and two more pairs of cables, and enjoy!