Sub Woofer hook up with McIntosh MC 501

Here is a possible solution
With a Vandersteen 2WQ you can safely take speaker
level out at the amp into the pair of 2WQs the reason is it has a safe 1/2 Mega ohm input Imp. You will also receive the benefits of
high Passing the main amps which will lower distortion
and dramatically clean up the clarity of your system and music.

Johnnyr

Spoke to Chuck Hinton at McIntosh, his feelings were it would probably be best not to run the sub and the mac together, although it may be possible depending on how they react to one another, it's not advisable. He did state that REL sub are setup to connect directly to an amp

I ran my Velodyne DD-15 from BAT-75SE power amp's speakers terminals, and the main speakers from the SAME amp terminals, using spades for one, and bananas for the other.
I don't think, you shoud use 4 ohms term. for the main speakers and 2 ohms for the subs.
Many people prefer speaker level signal to drive sub.