Conrad johnson pv10b to M&K subwoofer

You can't use the tape out because it isn't controlled by
the volume control, so the output would be fixed.

You can use a pair of "Y" adapters from the main
outputs. It will change the output impedance some, but I've
done this many times with excellent results. Your M&K sub
will need to have separate right and left inputs for this to
work correctly.

It does a L/R input in the subs. Would that damage my pre or amp by doing the Y?

No. All you are really doing is adding an extra set of outputs to the preamp with a "Y" adapter.

If your CJ PV10B preamp is tube, it may not be a great impedance match with the M&K MX-150 THX sub, as it only has a 15kohm input impedance, this is more suited to solid state preamp that have lower output impedances than tube preamps.

Cheers George