How do I get a speaker with the bass slam of my el cheapo ear buds...?

That amp is a beast and your speakers should be able to dig pretty deep.  I'm surprised you're not getting the bass response you'd like.

Oh, they go deep.  It's just the initial "hit" or attack of a kick drum, and the like, that I am questioning.  The Signature IIs are sealed, not ported, and I wonder if that has anything to do with it.  They also have the old poly mid drivers and bass woofers, which I assume are not as fast as modern drivers.

So, afterall, you want to let the phone to drive a series of state of the art preamp, amp and speakers and get a nice slam effect like the phone drivig a free earbud.  Thank you very much for your experiment.  It showed to all of us that it does not work.  :) 

By the way, I saw that you did purchase Krell FPB400 around Sep, 2014. You used to drive your Legacy speakers using a Nak receiver long long time ago.  It seems that you have a steady audio growth path with you. You even started a  “slam” topic before. You should have more knowlege than many (if not most) of us to answer your own question.  

mtrot,

I added a bit about earphones because you seem to like yours and millercarbon nicely explained what could be causing the difference you notice.

You seem to have decent home equipment but have you considered a possibility that you overall actually prefer the sound coming from phone through the earphones? These days, many people do. Many chase "perfect sound" while they could be enjoying more by accepting the fact that they like "imperfections". At the same time, some people simply prefer the sound through headphones. Chasing speakers to sound like headphones may not be that successful. They are inherently different.