Is my amp the problem?

Uh- all good suggestions, but before you do anything else, check to see that the woofers are in phase.

That is to say, if the red connection on the back of the amp is connected to the plus terminal of the speaker, that such is also the case with the other channel. This way both speakers are pushing and pulling in unison. Otherwise they are fighting each other, and you would have some pretty 'blah' bass!

@jimbones , FWIW, polarity is also known as absolute phase. I'm **not** talking about that, instead the phase of just one speaker as opposed to both. We might be talking the same thing, but since there is a bit of interpretation here I thought it a good idea to be certain.

The XO is a Pioneer SF 700. I will use it only as a low pass at approx 200hz. This is to compare with the mindsp re input impedance and output voltage. I am using a cap on the input of the Modwright as a hi pass.

Just as an experiment, what happens if you bypass the crossover and drive the preamp straight into the power amp driving the subs? The question is, how is the bass then?

Wow- that's a rather scathing indictment on a Crown class D amp. Can't even keep up with an aging and clearly limping conventional solid state amp. Sheesh.